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Next generation wireless LANs : 802.11n and 802.11ac (2nd ed.)
Perahia E., Stacey R., Cambridge University Press, New York, NY, 2013. 480 pp. Type: Book (978-1-107016-76-7)
Date Reviewed: Dec 17 2013

The terms wireless local area network (WLAN) and Wi-Fi are synonyms for the successful IEEE 802.11 family of standards. Many people do not realize how this standard has developed over the past 15 years. The original 802.11 standard allowed only gross data rates of up to 2 megabits per second (Mbit/s), whereas the most recent amendment, 802.11ac, allows gross data rates of more than 6 gigabits per second (Gbit/s). The book describes the techniques and underlying principles that made this steep increase possible.

The book is divided into three parts. Chapters 2 to 6 cover the physical layer of the current 802.11n-based WLANs. IEEE standard 802.11n builds upon the orthogonal frequency-division multiplexing (OFDM) technique. OFDM is used in several wideband systems, where signal fading is frequency dependent. An example of an OFDM system is the long-term evolution (LTE) mobile cellular system that was specified by the 3rd Generation Partnership Project (3GPP). OFDM principles, which were already used in the older 802.11a standard, are very briefly explained in chapter 2. New in 802.11n (when compared to 802.11a) is the possibility to use transmitters and receivers with multiple antennas in the multiple-input multiple-output (MIMO) mode. A MIMO system can be used to transmit independent data streams on different antennas. This is called spatial division multiplexing (SDM) and is well described in chapter 3. Other important multiple antenna techniques like receive diversity, spatial expansion, transmit beamforming, and space-time block coding are presented in more detail later in chapter 6.

In practical systems, devices based on older and newer standards are deployed together. Interoperability with legacy standards is therefore an important aspect of newer standards and was a functional requirement during the specification of 802.11n. It is described in great detail in chapter 4 and also in chapter 11.

The high-throughput amendment to the 802.11 WLAN standard is 802.11n. Chapter 5 presents several physical layer techniques to increase the data rate, for example, 40 megahertz (MHz) channel bandwidth, additional subcarriers, and specific preambles.

Chapter 7, which was added to the second edition, covers the new features of the 802.11ac physical layer. They include wider bandwidth of up to 160 MHz, the modulation and coding of spatial streams, and downlink multi-user MIMO.

The second part of the book is devoted to the medium access control (MAC) layer. The MAC layer allows several devices to share the wireless network concurrently. Chapter 8 gives an overview of the basic 802.11 MAC functions, whereas chapter 9 explains what MAC changes were necessary to improve 802.11 throughput.

The 802.11 MAC includes additional channel access mechanisms that go beyond the basic contention-based access protocol. These advanced access mechanisms are presented in chapter 10. Chapter 12 then goes into the details of the MAC frame format and serves as a reference for communications engineers. As could be expected, this part of the book is of less general interest than the first part.

The third part of the book covers specific techniques to increase data throughput, namely, transmit beamforming (chapter 13), multi-user MIMO (chapter 14), and fast link adaptation (chapter 15).

This well-written book is more than a summary of two WLAN standards. It is an introduction to the state of the art of wireless communications. It presents basic principles of advanced wireless communications systems that not only apply to WLANs, but also to other wireless communication systems like LTE and IEEE standard 802.16 (WiMAX).

The book also has some weak points. The mathematical framework is presented but not derived. Alternative solutions are not discussed, hence the rationale for the standardized solution sometimes remains unclear.

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Reviewer:  Klaus Galensa Review #: CR141818 (1402-0106)
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