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					Performance Enhancement of WLAN Using 802.11n and MIMO Technology                                                             1


         Performance Enhancement of WLAN Using 802.11n and
                         MIMO Technology
                        V. Vaithyanathan¹, Pethur Raj Chelliah² and Rathnakar Acharya³
                                        1
                                       Dept. of CSE, SASTRA University, Tanjavur
                                              2
                                               Wipro Technologies, Bangalore
                                         3
                                           Alliance Business Academy Bangalore
                      1                   2                            3
               E-Mail: vvn@it.sastra.edu, pethuru.chelliah@wipro.com, rathnakar.a@alliancebschool.ac.in


    ABSTRACT: 802.11n is IEEE wireless standards that significantly improve throughput and range of Wireless Local
    Area Networks(WLAN) compared with other 802.11 standards. It is expected to provide a throughput of over 100
    Mbps, which is twice that of 802.11g. This difference is because it is designed to operate in both 5 GHz and 2.4 GHz
    frequency band. The key issue in wireless communication is multi-path propagation. This multi-path propagation
    occurs when signal bounces buildings, walls and other obstacles and arrives at the receiver at different times and
    from different paths. If the time difference is large enough, the receiver gets confused and can’t interpret the signal
    causing retransmissions and therefore reducing the speed and data rate of the 802.11 networks. IEEE802.11n takes
    the advantages of multi-path propagation to increase throughput to speeds above 100 Mbps, by using MIMO or in
    other words multiple transmitters and multiple receive (MIMO) antennas. It uses spatial diversity to induce multi-path
    for the purpose of recombining the multiple signals to increase the signal gain, and channel multiplexing to send
    multiple signals using multiple antennas, therefore multiplying speeds, increases the range and enhances the
    performance.

    Keywords—IEEE 802.11n, Wireless Local Area Network (WLAN), Multiple Input Multiple Output (MIMO), Spatial
    Diversity.



INTRODUCTION                                                     architecture comparing to the Single Input Single Output
                                                                 (SISO) system. The rest of the paper is organized as

O     ne of the main issues for wireless communication by
      WLAN is due to the unimpeded path from the
transmitter to receiver. The real world is neither flat nor
                                                                 follows: Section II provides the information about IEEE
                                                                 802.11n standard. Section III we provide the overview of
                                                                 MIMO architecture and its role to mitigate the multi-path
empty, however, and physical barriers have long been the         fading. Section IV gives the details about the performance
nemesis of WLAN performance. The natural and man                 enhancement of WLAN using IEEE 802.11n standard and
made obstacles impede wireless signals, resulting                MIMO with result and finally the conclusion.
distortions, multipath fading and retransmission as a
consequences and ultimately effecting signal integrity and       IEEE 802.11N STANDARD
throughput. To compensate these earlier wireless
technologies used more power. To overcome these                  802.11n is an emerging IEEE standard that significantly
limitations IEEE have effectively revised the standard. This     improves throughput and range compared to earlier 802.11
new standards are now taking advantages of diversity             standards. Having higher data rate up to 100 Mbps, which
conditions to improve the performance and speed of               is twice the range of 802.11g, and also the backward
WLAN.                                                            compatibility with 802.11a/b/g, IEEE 802.11n device can
    This new standard is IEEE 802.11n, which uses similar        communicate and inter-operate with legacy 802.11a/b/g
modulation formats as that of IEEE 802.11g but has the           devices. In order to achieve the backward compatibility,
added advantages of applying spatial processing to improve       802.11n must support the three physical layer modulation
the performance. The technique is known as Multiple Input        techniques used by the older standards; Direct Sequence
Multiple Output (MIMO). This uses multiple antennas both         Spread Spectrum (DSSS), Complementary code keying
at transmitter and receiver. When the standard is considered     (CCK), Orthogonal Frequency Division Multiplexing
it will include MIMO option such as transmit beam                (OFDM).
forming, space-time block coding, cyclic delay diversity,           802.11n includes many features that improve
Maximum Ratio Combining (MRC) and intelligent antenna            throughput, range, reliability and efficiency. One of the
selection. The use of MIMO technology in IEEE 802.11n            important changes of character 802.11n uses MIMO
seems to be an attractive solution for the future wireless       technology to overcome the wireless propagation problem.
systems. In this paper, our discussion incorporates the          This is the first IEEE 802.11 standard to standardize use of
analysis of performance enhancement of MIMO                      MIMO antenna design, to significantly improve throughput
164                                                                                                         Mobile and Pervasive Computing (CoMPC–2008)


and range. 802.11n also incorporate many other features in
order to achieve superior performance. Comparison of the
different features and the throughput of IEEE 802.11a/b/g/n
are shown in the Table 1 and Fig. 1.

                       Table 1: IEEE 802.11 standard specifications
                                 802.11a       802.11b       802.11g    802.11n
  Max. data                     54 Mbps       11Mpbs        54Mbps     600Mbps
  rate
  Modulation                    OFDM          DSSS /        DSSS       DSSS/                                     Fig. 2: Multi-path signal transmission
                                              CCK           CCK        CCK/
                                                            OFDM       OFDM             Increasing the number of MIMO transmitters and
  RF Band                       5GHz          2.4GHZ        2.4GHz     2.4GHz/      receivers however holds even greater potential. As a simple
                                                                       5GHz
                                                                                    rule of thumb, the more radios you use the better is your
  Available                     580 MHz       83.5MHz       83.5MHz    83.5/580
  B.W                                                                  MHz
                                                                                    range and throughput up to a point we can obtain this
  No. of                        1             1             1          1, 2, 3 or
                                                                                    improvement at low cost in terms of both cost and power
  spatial                                                              4            consumption. By using multiple antennas both at
  streams                                                                           transmitter and receiver it boost the data transmission rate
  Channel                       20MHz         20MHz         20MHz      20MHz40      and quality of wireless signals. In doing so MIMO takes the
  width                                                                MHz          advantages of the various reflections seen by the receiver.
                                                                                    Space Division Multiplexing (SDM) is one of the
                                                                                    techniques used in MIMO, which spatially multiplexes
                      25                                                            multiple independent data streams transferred simulta-
                                                                                    neously within one spectral channel of bandwidth. MIMO
                      20
  Throughput (Mbps)




                                                                                    SDM can significantly increase data throughput as the
                      15
                                                                                    number of resolved spatial data streams is increased. Each
                                                                                    MIMO antenna requires a separate RF chain and Analog to
                      10                                                            Digital Converter (ADC). This increasing complexity
                                                                                    ultimately translates to higher implementation cost and
                       5                                                            higher performance systems are required. For each channel
                                                                                    the capacity increases as the channel bandwidth is
                       0                                                            increased. It can be represented by the Shannon‟s equation
                                                                                       C  B log 2 1  SNR 
                            5           10         15             20   25
                                             Simultaneous AP
                                                                                       Where C is the channel capacity and B is the channel
                                                        802.11n                     Bandwidth. From the expression it is clear that theoretically
                                                        802.11a/g                   capacity increase as the bandwidth is increased. The graph
                                                                                    in Fig. 3 indicates the increase in capacity as the bandwidth
                             Fig. 1: Average throughput/user                        increases.

                                                                                                           400
MIMO
                                                                                                           350
                                                                                         Capacity (Mbps)




MIMO is a technology that uses multiple antennas at the                                                    300
transmitter and receiver. MIMO exploits the fact that Radio                                                250
Frequency (RF) signals often reflected off of objects as in                                                200
Fig. 2 in their path, causing a phenomenon called multi-                                                   150
path fading. Spatial multiplexing is one of the techniques                                                 100
adapted in MIMO which helps to transmit multiple data                                                       50
streams at the same frequency but over different spatial                                                     0
channels. The spatial multiplexing takes advantages of the                                                          0    '5   10     15       20   25   30
multi-path phenomena to increase the effective channel                                                                             SNR (dB)
capacity without consuming additional spectrum. In effect
MIMO takes multi-path transmission and converts it from                                                                             20MHz
signal impairment into a signal enhancement. MIMO                                                                                   40MHz
makes a channel more spectrally efficient because spatial
multiplexing increases the baud rate/hertz ratio.                                                          Fig. 3: Capacity with respect to Bandwidth
Performance Enhancement of WLAN Using 802.11n and MIMO Technology                                                                    165


   Using wider bandwidth with OFDM offers significant                         The above wireless channel is modulated as
advantages when maximizing performance wider                                  The y  H x  n
bandwidth channels are cost effective and easily
accomplished with moderate increases in digital signal                        Where H is the channel matrix and n is the channel
processing (DSP).                                                          noise.
                                                                              For transmit/receive beamforming with the diversity of
PERFORMANCE ENHANCEMENT OF A                                               order MN, is considered as full diversity. On the other hand
WLAN USING IEEE 802.11N USING MIMO                                         the antenna gain is; max  M , N   antennagain  MN

The use of MIMO in IEEE 802.11n, not only improve the                         The data transmission capacity bits/channel use of a
reliability in data transmission, it also enhances the data                communication channel is the maximum throughput at
rate over wireless channels. With multiple antennas both at                which data can be sent over the channel. While maintaining
transmitter and receiver not only rejects fading; better yet it            a low probability of error, the capacity of a SISO channel
actually harness the fading itself in favor of increased                   having one transmit and one receive antenna,
throughput.                                                                                  E x2
    Consider the MIMO channel having multi-channel                            CSISO  log 2 1    
                                                                                             En 
                                                                                                 2
propagation between the transmitter and receiver is shown                                         
in the Fig. 4. Let M and N be the number of transmit and
receive antennas, respectively. The received signal in the                                      P 
                                                                              CSISO  log 2 1   2 
 th
i antenna is given by                                                                        2 
                                                                              Where P is the power of the signal transmitted
                                                                                    2
                                                                           PE x
                                                                                         2
                                                                                    Ex                    Es
                                                                              And             SNR 
                                                                                    En
                                                                                         2
                                                                                                       2
       Transmitter




                                                                              From the above expression it is clear that the capacity of
                                                                Receiver




                                                                           SISO system can be increased only if the transmission
                                                                           power is increased. In case of Wireless MIMO
                                                                                                    P 1 
                                                                              CMIMO  log 2 det 1     Q
                                                                                                 2 M 
                                                                                                      2

                            Fig. 4: MIMO System
                                                                                                   M           2

                     M                                                        where Power P   E x j the total transmission power
      yi   hij x j  ni where i = 1, 2, 3…N                                                      j 1

                     j 1                                                  radiating from the transmit antennas
      hij is the fading corresponding to the path from transmit                  HH * ....ifN  M 
                                                                                                  
                                                                              Q *                
antenna j to receive antenna i. n i is the noise corresponding                  
                                                                                 H H ....ifN  M 
to receive antenna i.                                                        „I‟     is     the      identity      matrix   of       size
               y1     x1    n1                                       min M , N   min M , N 
              y      x      n 
      Let      2      2      2
          y  .  x  .  n  . 
                                                                              „det‟ is the determinant of the matrix.
                                                                        Considering the Rayleigh distribution of the fading
              .      .      . 
               yN     xM    n N                                      yields
                             
                                                                                                             P 
      The channel matrix H is;                                                CMIMO  min M , N  log 2 1   2 
                                 h11 , h12 ,...........h1m                                              2 
                                                                                                                           CMIMO
                                 h22 , h22 ,..........h2 m                  The multiplexing gain is; MultiplexingGain 
                            H  .                                                                                          CSISO
                                                           
                                .                                           Under the same transmission power p, the multiplexing
                                 h , h ,........h                        gain is MultiplexingGain  m M , N 
                                 N1 N 2                 NM 
166                                                                  Mobile and Pervasive Computing (CoMPC–2008)


   Thus by using multiple antennas we can increase the      REFERENCES
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