Chapter 5
A survey on enabling wireless local area network technologies for smart cities
N. Omheni*
M.S. Obaidat†
Abstract
Over the previous 25 years, the development of the Internet and the progress of wireless technologies have made an incredible impact on lifestyle around the world. Together, these two features have changed the communication requirements in domestic, public, and business scenarios. At the beginning of this decade, wireless devices became affordable and Wireless Local Area Network (WLAN) rapidly became more secure and the standard technology to connect laptops, and later tablets and smartphones, to the Internet is growing quickly. Nowadays, the WLANs offer unlimited broadband practice to consumers that have been in the past provided simply to connect wirelessly equipment inside a short range. The most recent and the up-and-coming standards solve technology problems or append new features to the existing 802.11 technologies and will be expected to beat a number of standing troubles with 802.11.
The current trend of new-generation wireless networks is their use in the design and the building of smart cities. This technology guarantees better and healthier cities through the implementation of environment-based applications allowed by WLAN, robust environmental sensors, and low energy consumption. WLANs can be one of the ideal solutions to implement this kind of platforms.
This chapter focuses on this technology. The first part of this chapter illustrates the basics of the IEEE 802.11 standard. This includes a survey of WLAN concepts and terminology, Physical and Medium Access Control (MAC) Layers, applications of WLANs, and spread spectrum communication. In the second part of this chapter, we present the history behind the development of the standard and we detail the features of the IEEE 802 family that have been published. Then we will describe some upcoming standards and we discuss some key open problems of the IEEE 802.11 standard such as mobility, energy, security, and quality of service. The last part of this chapter focuses on the applications of WLANs to smart cities and homes, and the challenges posed.
Keywords
smart cities
Wireless Local Area Networks
MIMO
802.11ax
1. Introduction
IEEE 802.11 Wireless Local Area Networks (WLANs) became day after day the first tool for accessing broadband Internet all over the world. Slowly, their position as the leading carrier of wireless data traffic, is clearly observed. Statistics show that in the United States, the United Kingdom, Germany, Canada, South Korea, and Japan Wi-Fi has taken part with about 73% of the whole wireless traffic on Android smartphone in 2013; this percentage was 67% in 2012 [1]. This explosion may be thanks to the appearance of a broad range of customer devices, increasing network coverage, continuing technological evolution, and the development of worldwide standards. In the next, we give a view of paradigm change pushed by the evolution of the Wi-Fi technologies. The image, at its center, detains the initiative that Wi-Fi technology, which was in the beginning developed as an Ethernet cable substitute, has become a vital wireless technology all over the world, and will go on developing to stay pace with technical expansion and spectrum availability. In 1997, the first IEEE 802.11 standard was released by the IEEE 802.11 Working Group (WG), characterizing the two layers, Medium Access Control (MAC) and Physical (PHY). Earlier retained versions were IEEE 802.11a, b, g, and n [2] that operate at 2.4- and 5-GHz unlicensed bands. At its early phase, throughput is the main Wi-Fi challenge. After the first data rates defined by the original (1–2 Mbps), several important progresses have been made to increase throughput. In 1999, the publication of the amendment 802.11a was the first attempt to improve throughput. A novel mechanism named Orthogonal Frequency Division Multiplexing (OFDM) that enhances data rate was proposed. In OFDM, a radio signal is divided into multiple subsignals that are sent at the same time at different subcarriers. Afterwards, the IEEE 802.11n standard defines a data rate up to 600 Mbps over 10 times of 802.11a’s 54 Mbps. The main engines of these important enhancements are the implementation of many cutting-edge techniques of the time, such as frame aggregation, channel bonding, and Multiple-Input Multiple-Output (MIMO).
In order to achieve prolonged development, novelty, and vitality, Wi-Fi is expected to become more flexible and supple in dealing with its increasing and expanded use in a mixture of scenarios such as data rate and coverage, indoor and outdoor, individual and expert. For that reason, IEEE 802.11 WG and Wi-Fi Alliances (WFA) are discussing and publishing a number of advanced amendments that can be largely grouped into three wide classes: throughput enhancements, long-range extensions, and better ease of use.
2. Development of IEEE 802.11
802.11 group was initiated in 1990 and the IEEE 802.11 standard defines the WLAN was born in 1997. The original standard has defined three PHY layers for the same MAC layer corresponding to three types of 802.11 products:
• IEEE 802.11 Frequency Hopping Spread Spectrum (FHSS), which uses the spread spectrum technique based on frequency hopping;
• IEEE 802.11 Direct Sequence Spread Spectrum (DSSS), which also uses the spectrum spreading technique but on a direct sequence;
• IEEE 802.11 Infrared (IR), infrared type.
The IEEE 802.11 FHSS and IEEE 802.11 DSSS networks are wireless networks transmitting radio in the Industrial, Scientific, and Medical (ISM) band. Given their characteristics, these three types of products are not directly compatible. Thus, an IEEE 802.11 network interface card cannot communicate with an IEEE 802.11 DSSS NIC, and vice versa. Similarly, IEEE 802.11 IR can interact with an IEEE 802.11 FHSS or IEEE 802.11 DSSS.
The IEEE 802.11 standard has not remained static, and many improvements have been made to the original standard. These improvements now continue. Three new PHY layers have been added to the IEEE 802.11b, IEEE 802.11a, and IEEE 802.11g standards:
• IEEE 802.11b or Wi-Fi uses the same ISM band as IEEE 802.11 but with rates up to 11 Mbps. IEEE 802.11b is actually an improvement over IEEE 802.11 DSSS. Thus, a feature of IEEE 802.11b is to remain compatible with IEEE 802.11 DSSS.
• IEEE 802.11a or Wi-Fi 5 uses a new band, called unlicensed-National Information Infrastructure (U-NII) band located around 5 GHz. The flow rate of IEEE 802.11a can reach 54 Mbps, but losing compatibility with 802.11 DSSS and FHSS and 802.11b, due to the use of a different band.
• IEEE 802.11g uses the ISM band but with speeds up to 20 Mbps. This standard uses the OFDM waveform of 802.11a. But unlike IEEE 802.11a, IEEE 802.11g is compatible with IEEE 802.11b and 802.11 DSSS.
• IEEE 802.11n is an evolution of 802.11g that incorporates MIMO technique.
2.1. Protocol stack
The 802.11 standard describes the first two layers of the Open Systems Interconnection (OSI) model, namely, PHY layer and the data link layer. The latter is further subdivided into two sublayers, the Logical Link Control (LLC) and MAC. Fig. 5.1 shows the architecture of the model proposed by the WG 802.11 compared to the OSI model.
Figure 5.1 Layered Model of IEEE 802.11
The PHY layer of the 802.11 standard is the crossing point between the MAC layer and the support that allows exchanging information. Each PHY layer 802.11/a/b/g is divided into two sublayers:
• Physical Medium Dependent (PMD), which manages the encoding of data and performs modulation;
• Physical Layer Convergence Protocol (PLCP), which allows the listening of the carrier and provides Clear Channel Assessment (CCA) to the MAC layer indicating that the channel is free.
2.2. Frequency bands
The standard IEEE 802.11 uses frequencies in bands without a license. It uses free bands, which do not require authorization from a regulatory agency. Two unlicensed bands are used in 802.11a/b/g:
• ISM band
• U-NII band
2.2.1. ISM band
The ISM band used in 802.11/b/g corresponds to a frequency band around 2.4 GHz with a bandwidth of 83.5 MHz (2.4–2.4835 MHz). This band is recognized by key regulatory agencies such as the Federal Communications Commission (FCC) in the United States, European Telecommunications Standards Institute (ETSI) in Europe, and French Telecommunications Regulatory Authority (ART) in France. The released bandwidth differs according to the country (see Table 5.1).
Table 5.1
ISM Frequency Allocation by Country
| Country | Frequency Band (GHz) |
| United States | 2.400–2.485 |
| Europe | 2.400–2.4835 |
| Japan | 2.471–2.497 |
| France | 2.4465–2.4835 |
ISM, Industrial, Scientific, and Medical.
2.2.2. U-NII band
The unlicensed band U-NII is located around 5 GHz. It provides a bandwidth of 300 MHz (greater than that of the ISM band, which is equal to 83.5 MHz). This band is not continuous but it is divided into three separate subbands of 100 MHz. In each subband, the permitted emission power is different. The first and second subbands are for indoor transmissions. The third subband relates to outdoor transmissions. As for the ISM band, the availability of these three bands depends on the geographic area. The United States uses all subbands, Europe uses only the first two, and Japan uses the first. Organizations responsible for regulating the use of radio frequencies are as follows: the ETSI in Europe, Kensa-Kentei Kyokai in Japan, and the FCC in the United States.
2.3. Physical layer
As indicated earlier, the original 802.11 standard has defined three Basic PHY layers: FHSS, DSSS, and IR.
FHSS means a spreading band technique based on frequency hopping in which the ISM 2.4-GHz band is divided into 79 channels, each of 1-MHz wideband. To transmit data, the sender and the receiver agree on a specific sequence of jumps to be carried out on these 79 subchannels. FHSS layer defines 3 sets of 26 sequences, in total 78 possible sequences of jumps. The data transmission is done through a subchannel hopping another jump that occurs every 300 ms, in a predefined sequence. The latter is defined optimally in order to minimize the collision probability between multiple and simultaneous transmissions. If a station does not know the hopping sequence of channels, it cannot retrieve its data.
As the FHSS, DSSS divides the ISM band into subbands. However, the division here is 14 channels of 20 MHz each. The transmission is done only on a given channel. The bandwidth of the ISM band is equal to 83.5 MHz.
As well as these 802.11b utilizes a new PHY layer called High-Rate DSSS. 802.11a and 802.11g standards utilize OFDM. This technique can significantly increase the global debit of the network. A mixture of OFDM modulation techniques is recapitulated in Table 5.2. IEEE 802.11n uses OFDM and MIMO techniques together. The frequency band of most of IEEE 802.11 extensions is 2.4 GHz with 14 separate channels.
Table 5.2
OFDM PHY Layer Modulation Techniques
| Data Rate (Mbps) | Modulation Coding Rate Coded Bits/Sub | Coding Rate | Coded Bits/Subcarrier | Code Bits/OFDM Symbol | Data Bits/OFDM Symbol |
| 6 | BPSK | 1/2 | 1 | 48 | 24 |
| 9 | BPSK | 3/4 | 1 | 48 | 36 |
| 12 | QPSK | 1/2 | 2 | 96 | 48 |
| 18 | QPSK | 3/4 | 2 | 96 | 72 |
| 24 | 16QAM | 1/2 | 4 | 192 | 96 |
| 36 | 16QAM | 3/4 | 4 | 192 | 144 |
| 48 | 64QAM | 2/3 | 6 | 288 | 192 |
| 54 | 64QAM | 3/4 | 6 | 288 | 216 |
BPSK, binary phase shift keying; OFDM, Orthogonal Frequency Division Multiplexing; PHY, Physical; QPSK, quadrature phase shift keying.
802.11a version uses a set of channels varying from 36 to 161, although it uses a fixed channel center frequency equal to 5 GHz. In the United States the number of nonoverlapping channels is equal to 12. This number is 19 channels in Europe [3], while the number of nonoverlapping channels for IEEE 802.11b is limited to 3 only.
2.4. Medium access control layer
The MAC layer defines how a user obtains a channel to transmit when needed. It uses primitives provided by the PHY layer. It also proposes a standard interface to the LLC layer that can use all data transmission capabilities without knowing the specifics.
There are two access control functions: Distributed Coordinated Function (DCF) and Point Coordinated Function (PCF). The use of the PCF is optional and therefore it is little or not implemented in 802.11 hardware. The PCF consists of a centralized resource management. The access point (AP) orders transmissions and distributes the right to use medium.
DCF uses a distributed algorithm to manage access to channel. This algorithm uses the Carrier sense multiple access with collision avoidance (CSMA/CA) mechanism. It is completed by a random delay pulling mechanism before transmission (random backoff). Each station performs this algorithm locally to determine when it will begin its transmission. The CSMA/CA method is based on a carrier detection function to determine if the medium is busy or not.
In the contention-based mechanism named DCF if more than two stations try simultaneously to transmit, collision takes place. To avoid this kind of problem CSMA/CA can result in wrong medium information. This phenomenon is known as Hidden Node Problem where collision cannot be detected. If stations cannot communicate, the AP appeals to a Request to Send (RTS)/Clear to Send (CTS) mechanism.
2.5. IEEE 802.11 family and derived amendments
2.5.1. IEEE 802.11g
This version is operating in the 2.4-GHz band and the offered throughput is similar to 802.11a standard. The highest range of IEEE802.11g devices is a little larger than that of IEEE802.11b. However, the range in which users can reach full data rate speed (54 Mbps) is less than that of 802.11b.
2.5.2. IEEE 802.11e
IEEE 802.11e is a version of the IEEE 802.11 standard that introduces improvements in terms of Quality of Service (QoS) at the sublayer MAC of the OSI data link layer. This amendment was approved on September 22, 2005, and published on November 11 of the same year. IEEE 802.11e provides enhancements to the QoS plan for the transportation of voice, audio, and video through WLAN connection.
2.5.3. IEEE 802.11d
IEEE 802.11d specifies a mechanism based on the parameters of transmission related to airwaves signals to set up a mobile station respecting the regulations (regarding frequency ranges and authorized powers) through specific geographic territories and traversed policies.
2.5.4. IEEE 802.11f
The 802.11f is a proposal for the vendors of APs for better interoperability of different manufacturers’ products. It offers the Inter-Access Point Protocol, a roaming protocol, that allows a mobile user to switch seamlessly AP while traveling.
2.5.5. IEEE 802.11h
IEEE 802.11h is proposed to harmonize the standard IEEE 802.11a with regulatory requirements of the European Community on radio transmissions in the 5-GHz frequency band and energy savings. This amendment provides dynamic frequency selection mechanisms and control of the power transmission.
2.5.6. IEEE 802.11i
IEEE 802.11i deals with enhancing the security of exchanges in local computer network using a wireless connection. It introduces a robust security network (RSN) algorithm with improvements over Wired Equivalent Privacy (WEP) security mode recommended by the IEEE 802.11 standard. This amendment increased the authentication and encryption methods.
2.5.7. IEEE 802.11k
This version was designed for radio resource management. This amendment is proposed to improve the way of traffic distribution inside a wireless network. In a wireless environment, all clients try to connect with the AP that offers the best signal. This procedure can cause degradation of network performance because the majority of demands will be on a single AP. With IEEE 802.11k, if the AP having the best signal is overloaded, a wireless station will be connected to another underutilized AP.
2.5.8. IEEE 802.11j
This standard deals with the convergence of IEEE 802.11 American standard and European Hiperlan 2. The 5-GHz frequency band is used for both standards.
2.5.9. IEEE 802.11p
To communicate from vehicle to vehicle in a platoon, American Society for Testing and Materials (ASTM) adopted in 2002 a wireless standard called Dedicated Short-Range Communication (DSRC). In 2003, the IEEE WG has taken over the work to define a new standard dedicated to intercommunications vehicles, called wireless access in vehicular environments (WAVE) and also known as IEEE 802.11p. This standard uses the multichannel concept to ensure communications for security applications and other services of Intelligent Transport.
2.5.10. IEEE 802.11u
This standard deals with interworking with external networks. It allows higher layer functionalities to supply overall end-to-end solutions. The key goals of this standard are assisting network discovery and selection, enabling information exchange with external networks, and supporting emergency services.
2.5.11. IEEE 802.11v
This amendment was adopted in February 2011. It describes network terminal management standards: reporting, channel management, conflict management, and interference filtering service traffic.
2.5.12. IEEE 802.11r
The IEEE 802.11r, named Fast Basic Service Set Transition, was published in 2008. It allows a wireless device that moves to stay connected. 802.11r has been launched to try to alleviate the additional burden imposed by the security and QoS during handover.
2.5.13. IEEE 802.11s
IEEE 802.11s, known as the network Mesh [Wireless Mesh Networks (WMNs)] and derived from military research, allows connected entities to create a WMN in a dynamic manner. IEEE 802.11s extends the 802.11 MAC standard by introducing an architecture and a protocol that enable both unicast and broadcast transmissions by the use of radio-aware metrics.
2.5.14. IEEE 802.11w
IEEE 802.11w is the standard that defines management frames protected for the family of IEEE 802.11 standard. The aim of this amendment was to improve safety by ensuring the confidentiality of data contained in the management frames, via mechanisms that ensure data integrity and authenticity of data origin and anti-reexecution protection.
2.5.15. IEEE 802.11n
IEEE 802.11n, ratified in September 2009, achieves a maximum throughput of up to 450 Mbps on each of the working frequency bands (2.4 and 5 GHz). It improves the previous standards: IEEE 802.11a for the frequency band of 5 GHz, and IEEE 802.11b and IEEE 802.11g for the frequency band of 2.4 GHz. The purpose of this amendment is to increase the range and throughput of Wi-Fi networks and promises 300 Mbps (theoretical), and does not exclude the possibility to do better. To achieve this, 802.11n uses the MIMO technique. A radio signal transmitted between two points is supposed to go straight. In fact, there is nothing because the waves are reflected everywhere on walls, ceilings, furniture, etc., and the receiver does not receive a single signal but several offset signals depending on the length of each trip. MIMO will take advantage of these multipaths, considered rather disastrous in radio networks, to optimize the transmission between two points. The principle is to use multiple transmit antennas and multiple antennas for reception. It is not necessary that there is an equal amount on each side. Antennas transmit the same signals, out of phase so that the power transmitted at each time is maximal.
3. Smart city solutions
Smart City solution consists of smart industry, smart government, and smart life. It mixes city management, company development, and way of people life in a ubiquitous Information and Communication Technologies (ICT)-based system through the full use of cloud computing, communications network, and information cooperation. Smart city supports stable urban progress and best possible resource exploitation, improves urban intelligence coverage, and boosts operational effectiveness and citizen approval. Fig. 5.2 shows an example of a smart city solution.
Figure 5.2 A Smart City Solution Example
Smart industry encourages a city’s permanent economic development as good as digital and intelligent advances to draw tactical investment and complicated companies to its high-tech squares. A good example of the smart industry solution can be Smart Park that offers professional IT services and cloud-based data centers to assist enterprises to build up businesses and urban economy.
As the core of urban managing, a public government can find solutions to the imposed challenges from public safety, emergency handling, urban transport, energy consumption, and green safety. Smart Government makes use of a cloud-based data core to store and share information, and cooperates with various sectors to enhance resource utilization and optimize governmental efficiency.
Smart life makes easy smart addition among intelligent applications and interactive systems for real-time communication, education, and healthcare. Smart life picks up a city’s service point and citizen fulfillment, rising quality of life. Fig. 5.3 summarizes all smart city solutions.
Figure 5.3 Smart City Solutions
3.1. Smart cities based on WLAN use cases
The study of the sub–1-GHz license-exempt bands [aside from TV white spaces (TVWS)] by the IEEE 802 LAN/MAN Standards Committee in 2010 showed that this spectrum is highly promising for outdoor WLAN transmission. Due to the shortage of the existing spectrum, using broadband is not allowed particularly in 802.11n and 802.11ac. However, the new modulation techniques and coding schemes (MCS), proposed in the two amendments 802.11ac and 802.11ah, can offer a rate that can exceed 300 Mbps in a good channel condition. In parallel, sub–1-GHz license-exempt bands allow to have better propagation behavior in outdoor situation than original for Wi-Fi 2.4- and 5-GHz bands, which extend transmission range over 1 km in normal conditions.
3.1.1. Smart sensors and meters
Smart sensors and meters using efficient modulation and coding schemes with good propagation characteristics and moderately narrow bands permit to introduce a new ability for sensor networks, which excels Bluetooth and ZigBee in coverage, throughput, and power consumption. The majority of considered use cases are geared toward sensing applications [4] such as:
• smart grids;
• smart meters (water, gas, and power consumption);
• automation of industrial practice (pharmacy, iron, steel, and petroleum refinement);
• agricultural and environmental monitoring (forest fire detection, pollution, humidity, temperature, water level, etc.);
• older care system (fall discovery, pill bottle check);
• indoor healthcare and fitness room.
In these use cases, an AP periodically sends out small packets to hundreds of equipment (sensors/actors). Many stations competing for the channel can result in collisions. Wide transmission range results in elevated interframe spaces and high overhead. The real throughput in these use cases does not exceed 1 Mbps. Another limit is the power consumption, as sensors are frequently battery powered. These limits must be carefully studied by standardization institutions in the future [5].
3.1.2. Extended-range hotspot
The characteristics of the sub–1 GHz such as the high data rates and the extended transmission ranges make this band very suitable for traffic off-loading inside mobile networks and for expanding hotspot range. Although 802.11n and 802.11ac throughput is equal to or even elevated than the new mobile network rates [Long-Term Evolution (LTE)], it can be utilized for off-loading in outdoor cases owing to short transmission range. On the contrary, the extension of the transmission range in 802.11ah will give a greater value, particularly in countries with wide existing S1G channel, for example, the USA [6]. In this direction, the 802.11 ah must supply at least one operation mode capable to attain a greatest aggregate multistation throughput of 20 Mbps at the PHY layer.
3.1.3. Backhaul aggregation
The final use case to make network technology for smart cities concerns backhaul link connecting IEEE 802.15.4g devices and distant servers [7]. This type of device is extensively used in industry and it is characterized by low energy consumption and very low data rates.
IEEE 802.15.4g routers collect information from devices and transmit them to the servers through 802.11ac links. These links may also be used to transmit surveillance videos obtained from autonomous cameras. Fig. 5.4 shows an enabling networking technology use case for smart cities.
Figure 5.4 Enabling Networking Technology Use Case for Smart Cities
3.2. Enabling WLAN technologies for smart cities
Next generations of WLANs have evolved by incorporating the latest technological advances in the field telecommunication. The IEEE 802.11n standard chooses Single-user MIMO (SU-MIMO) technology, packet aggregation, and channel bonding. Those methods were more expanded in the IEEE 802.11ac standard that was published in 2013 to reach data rates about 7 Gbps. In addition, upcoming standards such as the IEEE 802.11af and the IEEE 802.11ah are expected to supply new WLAN application scenarios including long-range communication solutions, cognitive radio, advanced power-saving methods, and maintenance for Machine-to-Machine (M2M) equipment.
3.2.1. IEEE 802.11ad
The IEEE 802.11ad, called also WiGig, is a pretty new standard that was published in December 2012. Its requirement includes a “fast session transfer” mechanism [3]. The IEEE 802.11ad offers the capacity to change bands guaranteeing that active devices are regularly best connected in order to supply good concert and range criteria. Many clients in a wide deployment can keep top data rate performance, without causing interference with one another or having to normally gash bandwidth similar to the legacy frequency bands [8]. The IEEE 802.11ad uses frequencies in the millimeter-range microwave Wi-Fi and provides radio coverage of a few meters. The goal of this very small range is to exchange a high volume information, for example, HD video transfers.
The amendment applies a MAC layer standard that is common with existing 802.11 standards to allow seamless session handoff between 802.11 WLAN using the 2.4- and 5-GHz bands and those working in the 60-GHz bands. On the other hand, new specifications related to 802.11ad MAC layer have been proposed such as synchronization, authentication, association, and channel access required for the 60-GHz band operation. The key features of this standard are outlined in Table 5.3.
Table 5.3
IEEE 802.11ad Key Features
| Parameter | Description |
| Operating frequency range | ISM band: 60 GHz |
| Maximum data rate | 7 Gbps |
| Typical distances | 1–10 m |
| Modulation | Single carrier and OFDM |
| Antenna technology | Operates beamforming |
ISM, Industrial, Scientific, and Medical; OFDM, Orthogonal Frequency Division Multiplexing.
The 802.11ad system operates in the ISM band and frequencies are between 57 and 66 GHz according to geographic location as shown in Table 5.4. The PHY layer of the 802.11ad supports three modulation techniques: spread spectrum modulation, single carrier (SC) modulation, and OFDM modulation. The used OFDM modulation allows achieving high throughput while maintaining excellent resistance alongside multiple path propagation.
Table 5.4
60-GHz Global Frequency Allocation
| Region | Allocation (GHz) |
| European Union | 57.00–66.00 |
| USA and Canada | 57.05–64.00 |
| South Korea | 57.00–64.00 |
| Japan | 59.00–66.00 |
| Australia | 59.4–62.90 |
The key signals specified by the 802.11ad PHY amendment are as follows [9]:
• Control PHY: This signal utilizes code spreading, differential encoding, and binary phase shift keying (BPSK) modulation to provide control. The Control PHY allows elevated levels of error detection and correction with a comparatively low debit.
• SC PHY: The modulation techniques used for this type of signal are quadrature phase shift keying (QPSK), BPSK, and 16-quadrature amplitude modulation (16QAM) on a concealed carrier positioned on the middle of channel. The symbol rate of this signal has been set at 1.76 Gsym/s and a mixture of error coding types is defined.
• OFDM PHY: This signal involves using multicarrier modulation technique to supply elevated modulation concentrations and elevated throughput.
• Spread QPSK: This 802.11ad signal engages in OFDM carrier pairs with which information are modulated. A maximum separation between the two carriers is needed in order to get better strength of the signal in case of selective fading of frequencies.
• Low Power SC PHY: This signal involves the use of a SC to reduce the energy utilization. It is planned for little battery equipment that is not clever to maintain the processing necessary for the OFDM design.
3.2.2. IEEE 802.11ae
The 802.11ae amendment has mainly two new mechanisms for processing management frames: a new mechanism for the supple prioritization of management frames and a new signaling algorithm for the exchanging frame prioritization policies. The prioritization mechanism is entitled the QoS management frame (QMF) service. QMF is a policy that gives a mapping between the management frame types and subtypes and the enhanced distributed channel access (EDCA) mechanism where the QoS is supported by introducing different access categories (ACs; EDCA ACs). In this way, all management frames are transmitted in an AC as specified by the existing QMF policy (Fig. 5.5).
Figure 5.5 QMF Operation
This amendment defines a default QMF policy. But usually the QMF policies are flexible, and they can be recognized and updated using a signaling protocol defined in 802.11ae. So, this aspect permits the QMF service to be adjusted to vendor application necessities. The procedure of the signaling protocol runs according to the type of network: mesh or infrastructure. Here, it should be noted that the use of QMF is not allowed in an independent basic service set (IBSS, ad hoc) network by the IEEE 802.11ae. In the infrastructure mode, QMF policy is defined by the AP for the entire basic service set (BSS). In the mesh network, a mesh station (MS) can set the QMF policy with another MS on a per-link basis. The QMF policy can be broadcast into existing frames like beacons or using new dedicated frames as mentioned in Table 5.5.
Table 5.5
Default QMF Policy (Omitted Frames Are Assigned to BE) and Policy Dissemination Frames
| Type of Frame | Description | QMF Access Category | Dissemination of QMF Policies | |
| Infrastructure BSS | Mesh BSS | |||
| (Re) Association Request/Response | Handover between APs | VO | Yes (in responses) | No |
| Probe Request (individually addressed) | Scanning initialization (unicast) | VO | No | No |
| Probe Response | Scanning result | BE | Yes | No |
| Beacon, ATIM, Disassociation, Authentication, Deauthentication | Network maintenance | VO | Yes (beacon) | No |
| Channel switch announcement | Initialization of channel switching | VO | No | No |
| Extended channel switch announcement | Initialization of extended channel switching | VO | No | No |
| QoS frames | QoS signaling (eg, TSPEC exchange) | VO | No | No |
| Measurement pilot | Basic scanning information | VO | No | No |
| Tunneled Direct-Link Setup Discovery Response | Part of direct-link setup | VO | No | No |
| Fast BSS Transition | Prehandover setup to speed up the handover process | VO | No | No |
| High-Throughput frames | Support for data rates greater than 100 Mbits/s | VO | No | No |
| Security Association Query frames | Procedure for robust management frame protection | VO | No | No |
| QMF Policy and QMF Change Policy | Dedicated frames for the dissemination of QMF policies | BE | Yes | Yes |
| Hybrid Wireless Mesh Protocol Mesh Path Selection | Path selection in mesh BSS | VO | No | No |
| Congestion Control | Congestion information dissemination in Mesh BSS | VO | No | No |
| Self-Protected frames | Management of security associations | VI | No | No |
| Disablement of Dynamic Station Enablement | Related to the operation in the 3650- to 3700-MHz band in the United States | VO | No | No |
AP, access point; BSS, basic service set; QMF, QoS management frame; QoS, Quality of Service; ATIM, announcement traffic indication map; TSPEC, traffic specification, BE, Best Effort.
3.2.3. IEEE 802.11ac
The aim of this standard is to get better Wi-Fi customer practice by offering considerably higher data rates for current application fields, and to permit devices operation below 6 GHz with distribution of various data flows. With throughput more than 1 Gbps and numerous innovative characteristics, data rates and application offered by IEEE 802.11ac assure to be like those of current wired networks. The 802.11ae amendment enhances the existing 802.11n version to attain the Very High Throughput (VHT). To achieve this purpose, the 802.11ac has added a number of optional factors to those that are obligatory. The optional factors are modulation, channel bandwidth, and number of spatial streams.
802.11ac devices are operating in the 5-GHz band. The alternative to limit handling in this frequency band is principally forced by the wider channel bandwidth requirements for 802.11ac. As the bandwidth augments, channel layout becomes challenging, mainly in the crowded 2.4-GHz band. As in the case of the relatively large 5-GHz band, devices will require to adjust regular radio tuning abilities to exploit the offered resources.
As well as the 20- and 40-MHz bands used by the majority of 802.11n devices today, the 802.11ac amendment specifications define a compulsory 80-MHz channel band. The main advantage of this larger bandwidth is to double the PHY layer rate above that of 802.11n at insignificant charge boost for the chipset producer and to support new applications. Another optional 160-MHz channel bandwidth is specified in the amendment, which can be also contiguous or noncontiguous (80 + 80 MHz).
The advantage of 160-MHz PHY, compared with 40/80-MHz transmissions, is the reduction of the requirement complexity that lets devices reach gigabits per second wireless throughput and support new applications. On the other hand, 160-MHz bandwidth in the 5-GHz spectrum is not available all over the world, and implementations to support these specifications will be probably expensive. Fig. 5.6 and Table 5.6 illustrate the spectral mask specifications for 802.11ac devices.
Figure 5.6 Spectral Mask Specifications for 802.11ac
Table 5.6
Spectral Mask for 20, 40, 80 and 160 MHz
| Channel Size (MHz) | f1 (MHz) | f2 (MHz) | f3 (MHz) | f4 (MHz) |
| 20 | 9 | 11 | 20 | 30 |
| 40 | 19 | 21 | 40 | 60 |
| 80 | 39 | 41 | 80 | 120 |
| 160 | 79 | 81 | 160 | 240 |
The modulation technique used in 802.11ac applies the 802.11n OFDM. Specially, the two 802.11n and 802.11ac technologies involve device supporting QPSK, BPSK, 16QAM, and 64QAM modulation. On the other hand, two main dissimilarities can be noticed compared to the IEE 802.11n standard. Primarily, the 802.11ac comprises an approved constellation mapping improvement [optional 256QAM (3/4 and 5/6 coding rates)]. The 256QAM modulation was defined as an optional mode, as opposed to an obligatory mode. Second, the number of defined MCS indices is really minimized.
Many cases of 802.11ac scenarios between an AP and another 802.11ac user device can be defined as illustrated in Table 5.7.
Table 5.7
Examples of 802.11ac Configurations
| Configuration | Typical Client (STA) Form Factor | PHY Link Rate | Aggregate Capacity |
| 1-Antenna AP, l-antenna STA, 80 MHz | Mobile Phone, Mobile Entertainment Device | 433 Mbps | 433 Mbps |
| 2-Antenna AP, 2-antenna STA, 80 MHz | Tablet, Laptop, Networked Game Console | 867 Mbps | 867 Mbps |
| 1-Antenna AP, l-antenna STA, 160 MHz | Mobile Phone, Mobile Entertainment Device | 867 Mbps | 867 Mbps |
| 2-Antenna AP, 2-antenna STA, 160 MHz | Tablet, Laptop, Networked Game Console | 1.73 Gbps | 1.73 Gbps |
| 4-antenna AP, four 1-antenna STAs, 160 MHz (MU-MIMO) | Mobile Phone, Mobile Entertainment Device | 867 Mbps to each STA | 3.47 Gbps |
|
8-Antenna AP, 160 MHz (MU-MIMO) • One 4-antenna STA
• One 2-antenna STA
• Two 1-antenna STA
|
TV Set-Top Box, Tablet, Laptop, Networked Game Console, Mobile Phone | 3.47 Gbps to 4-antenna STA 1.73 Gbps to 2-antenna STA 867 Mbps to 1-antenna STA |
6.93 Gbps |
| 8-Antenna AP, four 2-antenna STAs, 160 MHz (MU-MIMO) | TV Set-Top Box, Tablet, Laptop, PC | 1.73 Gbps to each STA | 6.93 Gbps |
AP, access point; MU-MIMO, Multiuser Multiple-Input Multiple-Output; PHY, Physical; STA, Station
3.2.4. IEEE 802.11ah
IEEE 802.11ah is a promising WLAN standard that introduces a WLAN system operating at sub–1-GHz license-exempt bandwidths. The draft standard IEEE 802.11ah-D1.0 [10] was published in October 2013 and the work will be completed by 2016 [11].
The IEEE 802.11ah PHY layer used the same basis as the 11ac standard and is adapted to available S1G bandwidth. The channel bandwidths supported by the 11ah are 10 times narrower than those in .11ac. These channels are 1, 2, 4, 8, and 16 MHz, where just 1- and 2-MHz channels are obligatory. After numerous S1G regulation studies in many countries, this amendment was confronted by the difficulty that the offered bandwidths for S1G ISM transmission differ from one country to another; the present draft of the standard defines which channels shall be used in the following countries: the United States, Japan, Europe, South Korea, China, and Singapore. Fig. 5.7 shows channelization opportunities for the United States [12]. PHY properties are similar to those of the .11ac: the use of OFDM technique, MIMO, and Downlink Multiuser MIMO (MU-MIMO).
Figure 5.7 US Channelization
The amendment defines some standard data rates for a variety of bandwidths and MCSs as shown in Table 5.8. They can be enhanced by minimizing the OFDM symbol period and applying numerous spatial streams.
Table 5.8
Some Regular Data Rates for Various Bandwidths and MCSs
| MCS | 1 MHz | 2 MHz | 4 MHz | 8 MHz | 16 MHz |
| MCS0 | 0.3 | 0.65 | 1.35 | 2.925 | 5.85 |
| MCS1 | 0.6 | 1.30 | 2.70 | 5.850 | 11.70 |
| MCS2 | 0.9 | 1.95 | 4.05 | 8.775 | 17.55 |
| MCS3 | 1.2 | 2.60 | 5.40 | 11.700 | 23.40 |
| MCS4 | 1.8 | 3.90 | 8.10 | 17.550 | 35.10 |
| MCS5 | 2.4 | 5.20 | 10.80 | 23.400 | 46.80 |
| MCS6 | 2.7 | 5.85 | 12.15 | 26.325 | 52.65 |
| MCS7 | 3.0 | 6.50 | 13.50 | 29.250 | 58.50 |
| MCS8 | 3.6 | 7.80 | 16.20 | 35.100 | 70.20 |
| MCS9 | 4.0 | – | 18.00 | 39.000 | 78.00 |
| MCS10 | 0.15 | – | – | – | – |
MCS, modulation techniques and coding schemes.
In legacy 802.11 infrastructure networks, the MAC header length that contains three MAC addresses is 30 bytes. The field Frame Check Sequence (FCS) adds 4 bytes. Therefore, for a 100-byte payload (messages), MAC header overhead is above 30%. For shorter messages, the overhead is still considerable.
Several limitations have been mentioned in the existing WLAN versions regarding power saving especially when the number of devices in the network increases. One of the challenges is long length of the beacon frame because of the extreme length of the partial virtual bitmap in TIM (Traffic Indication Map) IE (Information Element). Additionally, if the quantity of the buffered traffic is too important to be admitted inside a beacon interval, some power-saving machines unavoidably stay in a wake status to achieve the receptions of their buffered data.
To cope with these limitations, the 802.11ah amendment introduces a new technique called TIM and page segmentation. An AP divides the whole partial virtual bitmap equivalent to one page into numerous page segments, and each beacon is in charge for carrying the buffering status of only a one page segment. Next, each power-saving station awakes at the transmission moment of the beacon that takes the buffering information of its segments. A new information element named segment count IE is defined to bring segmentation information. Fig. 5.8 illustrates an example of segmentation.
Figure 5.8 An Example of TIM Segmentation
Moreover, the IEEE 802.11ah defines a new mechanism, named Multicast AIDs (MIDs), to multicast groups. Each station asks for MID from the AP if it fits into a multicast group. In the demand, the device must indicate its group MAC address and its preferences for listen duration. Since different stations of the same group may have diverse preferred listen periods and different power restrictions, the amendment permits to have many MIDs for each group. When the AP buffers data to a multicast group, it puts the equivalent bit in TIM so all machines of the group stay awake to receive data via the downlink; however, other stations do not squander power.
3.2.5. IEEE 802.11af
IEEE 802.11af, also called White-Fi and Super Wi-Fi [13], is a wireless standard in the 802.11 family that permits WLAN operating in TVWS spectrum in the very-high-frequency (VHF) and ultrahigh-frequency (UHF) bands. The standard was accepted in February 2014 [14]. The new specifications of IEEE 802.11af are conceived to supply geolocation server access to formerly unavailable, unused, or underused frequencies to allow customers worldwide to benefit from unused or underused spectrum, based on location and time of day. IEEE 802.11af uses 6-, 7-, and 8-MHz channels, allowing thereby compatibility with existing international TV band allocations. Operation may be in one to four channels, both contiguously and in two noncontiguous blocks, offering a means for equipment to collect enough bands in a fragmented TV band spectrum to give high throughput.
TVWS is for the moment available spectrum resources in VHF and UHF bands that are initially licensed to the TV broadcasters and wireless microphones, which can be opportunistically used by unlicensed devices only if no destructive interference is forced on the licensed users. TVWS operate in 470–790 MHz in Europe and the United Kingdom, and noncontinuous 54–698 MHz in Korea and the United States, as illustrated in Fig. 5.9.
Figure 5.9 Frequency Bands of IEEE 802.11af
The 802.11af amendment presents the WLAN operations at TVWS to bring the so-called “Super Wi-Fi.” Due to the good propagation characteristics of such low-frequency bands in contrast to 2.4- and 5-GHz bands, comprising lowered path loss and improved wall-penetrating ability, the Super Wi-Fi signal can be transmitted over longer distances than the original Wi-Fi signal. Consequently, over-the-air broadband access can be applied at minor cost by deploying 802.11af APs much less densely. IEEE 802.11af authorizes a function under the firm regulatory constraints, based on location-aware equipment and Geolocation Database. IEEE 802.11af makes use of most advanced techniques of 802.11ac such as MU-MIMO. Table 5.9 presents the main characteristics of this standard.
Table 5.9
IEEE 802.11af Key Features
| Parameter | Description |
| Operating frequency range | 470–510 MHz |
| Channel bandwidth | 6 MHz |
| Transmission Power | 20 dBm |
| Modulation format | BPSK |
| Antenna Gain | 0 dBi |
BPSK, binary phase shift keying.
3.3. Examples of smart city services and applications
Examples of hyperconnected smart cities are illustrated in Ref. [15] and comprise Songdo in South Korea, Masdar in the United Arab Emirates, more than dozens of cities in China, and a lot of cities in the world. In the United Kingdom, Bristol City Council is currently building a smart city in the context of the Sensor Platform for HealthCare in a Residential Environment project (SPHERE project, 2013–18) to supervise the health and well-being of residents in domicile [16]. Bristol also has a more wide smart city plan targeting home healthcare services.
In the United Kingdom, Love Clean Streets [17] is a new application that allows Internet-connected peoples to use their mobile phones’ built-in camera and Global Positioning System (GPS) to back up and inform their local authorities about any neighborhood or environmental focuses or offenses when they are not at home. Users are able to consult later online the Love Clean Streets website to check their report status. City committees across the United Kingdom are responding on time to citizens’ report request through the Love Clean Streets mobile application.
A new project called the “Internet of Everything” was launched in Barcelona [18]. The “Internet of Everything” plays the role of the backhaul around which scientific projects are being undertaken in Barcelona, rather than doing initiatives in other places in silo. Around 500 km of subversive fiber network is being established as the city performs regular repairs to its road, rail network, and other underground services, which can diminish equipment installation costs considerably.
4. Requirements
Requirements of smart city design and achievement can be summarized in the following points:
• Interoperability: An obvious tendency is the interconnection of all the possible data sources inside a global infrastructure to be able to support any new service.
• Scalability: Networks must have the ability to accept anew services and a large number of users that is about to change.
• Fast deployment: The deployment of new networks and updating existing infrastructure need to be faster and easier as possible in order to encourage the quick installation of equipment.
• Robustness: Life in a smart city requires a number of services. Consequently, the communication should have a certain level of robustness to give guarantees in terms of availability under normal conditions and also extreme conditions.
• Limited power consumption: In obedience to rules posed in the field of green communications and recent activities of smart cities, installed infrastructure and devices must have a minimum impact on the environment and should be characterized by low energy consumption and to reduce their operating and management costs.
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