Olivier Zoude Course BEng Computer Networking · 2015. 2. 1. · Module – CT6052: Wireless...

Module – CT6052: Wireless Networks (CISCO) / Coursework Report: Investigation on 802.11n / By: Olivier Zoude - ID 10034346 / Confidential Document: LondonMet University 2013 – 2014

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Faculty of Life Sciences & Computing

Student Name Olivier Zoude

Student ID 10034346

Course BEng Computer Networking

Student Email [email protected]

Module Code CT6052

Module Title Wireless Networks (CISCO)

Project Title Investigation on 802.11n

Submission

Date 10/01/2014

Module Tutor’s

Name & Email

Mr Harry Benetatos [email protected]

mailto:[email protected]:[email protected]


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Table of Contents

Abstract................................................................................................................3

1 - Introduction....................................................................................................3

2 - Literature Review...........................................................................................4

2.1 History of IEEE 802.11 and evolution of IEEE 802.11a/b/g/................4 2.2 High Throughput and IEEE 802.11n Development......................................5

2.3 Features overview of IEEE 802.11n. ...........................................................8

3 - Approaches and Methodology..................... ................................................10

3.1 Physical Layer (PHY) extension function ..................................................10

3.2 Medium Access Control (MAC) extension function...................................11

3.3 PHY system model function........................................................................12

3.4 MIMO system model function.....................................................................12

4 - 802.11n performance limitations and propositions for improvement..........14

4.1 Limitations of 802.11n performance............................................................14

4.2 Propositions to improve 802.11n performance............................................15

5 – Conclusion...................................................................................................15

6 - References....................................................................................................16


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Abstract

The aim of this project is to investigate on 802.11n which is an amendment of 802.11

standards attending to create the same working environment as per the wired network

performance with the mobility of wireless capacity and capability. The 802.11n allows higher

throughput, increase the coverage and the reliability of the Wireless Local Area Network

(WLAN) transmission.

The improvement applied by the 802.11n on 802.11 standards is based on the use of multiple

inputs and multiple outputs (MIMO) technique from the transmitter antenna to the receiver

antenna over the physical layer (PHY). This amendment is also the use of subcarrier

transmission scheme called Orthogonal Frequency Division Multiplex (OFDM). With the

used of wider bandwidth, and from the improvement of transmission efficiency via MIMO,

and the PHY, the 802.11n is able to achieve a throughput of up to 600 Mbps. To emphasize

the 802.11n investigation, the method of channel modelling will be discussed, also the MIMO

and OFDM techniques will be discussed to analyse the importance and impact of amendment

operated over the PHY function.

1 - Introduction

The 802.11n, 802.11 standards new generation, has started been implemented by the Task

Group (TGn) in late 2003 and took seven years to finish. The group mission was to

investigate standardized modification of both 802.11 PHY and Medium Access Control

(MAC) modes operation to reach a speed of at least 100 Mbps. Then the Institute of

Electrical and Electronics Engineers 802.11 (IEEE 802.11) set of MAC and PHY

specification of implementing Wireless Local Area Network (WLAN), committee for 802.11,

has approved the 802.11n and was published in October 2009. 802.11n operating at a

maximum throughput rate from 54 Mbps to 600 Mbps is the amendment improving the

802.11 standards by adding MIMO antennas on both side data transmitter and receiver.

802.11n features had two major impacts over 802.11 standards improvement, which are

effectiveness and robustness of the wireless transmission via PHY and the implementation of

better efficiency of MAC format. Therefore to understand the 802.11 standards improvement

to obtain the 802.11n, our project aim will be to:

- Investigate on 802.11n by identifying the key feature that the new 802.11 generation standards implemented, explain how and why it over performs the standard

802.11a/b/g.

Also to achieve the above aim, our objectives will be to:

- Research the related background information to 802.11 standards and study their different variant evolution amendment.

- Investigate on the new technology used to implement the 802.11 standards to obtain the 802.11n for effectiveness and robustness through data transmission.

- Elaborate over PHY, OFDM and MIMO implementation and understand that their improvement is the major enhancement into the 802.11n amendment.

The aim and objective described above will allow us to comprehend the critical need of

802.11 standards improvement and the highly performing technology put into place to reach

the new wireless generation: the 802.11n. But the 802.11n having obvious limitations over its


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performance, we will therefore through discussions elaborate some propositions to improve

its performance.

2 - Literature Review

2.1 History of IEEE 802.11and evolution of IEEE 802.11a/b/g/...

“In 1985, the Federal Communications Commission (FCC) decided to open up the Industrial

Scientific and Medical (ISM) bands for use by unlicensed low-power communication devices

using spread-spectrum modulation methods” (Ref 1). This mean the band from 2.4-2.5 GHz

would be available for individual use on non-license application, attracting a significant

interest over low-power devices communication using spread spectrum as data transfer

medium. This new unveiled the up-and-coming wireless devices developer and led to a less

standardized 802.11environment. Therefore in early 1990s the IEEE realized that wireless

communication infrastructure environment needed to be standardized to meet the market

growing demand (Ref 2). Then an executive committee was put in place to regulate the

WLAN standard. Initially the committee defined the specification of IEEE 802.11 standard

working environments with the combination use of MAC and PHY communicating with the

802.2 Logical Link Control (LLC). Table 2 shows in detail the primary IEEE 802.11 standard

up to 802.11n specifications (Ref 3).

The first WLAN standard ratified and accepted on the market was the 802.11b using the

Complementary Code Keying (CCK) and the Direct-Sequence Spread Spectrum (DSSS) as

modulation technique. In the same period the Wireless Ethernet Compatibility Alliance

(WECA), a non-profit association for Wireless Fidelity (Wi-Fi) promotion (Ref 4), was

created, then no long after the 802.11a using the more complex OFDM waveforms operating

in 5GHz Radio Frequency (RF) band range was adopted. In 2003 the 802.11g allowing the

use of DSSS or CCK or OFDM modulation technique was ratified. After many amendments

the 802.11a, 802.11b, 802.11d, 802.11e, 802.11g, 802.11h, 802.11i, and 802.11j, were all

rolled into one consolidated standard – IEEE 802.11 – 2007 and are part now to the baseline

standard of the 802.11 WLAN (Ref 5).


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(Fig 2) Evolution Timeline of 802.11 standards

2.2 High Throughput and IEEE 802.11n Development

“Before 802.11n, the transmitter and receiver were Single Input/Single Output (SISO)

devices” (Ref 6). Observing the increasing high demand of bandwidth from wireless users,

the IEEE set out to exceed the 54Mbps as an upper data rate and created the high throughput

task group or the Task Group n (TGn) in September 2003. The group worked on the MIMO

data transmitting method project allowing the 802.11n to use the multiple separated data

stream (Fig 3), to increase the data transfer rate to at least 100 Mbps. This project scope will

be achieved by standardized modification on both 802.11 PHY and MAC layer which will

effectively increase the 802.11 throughput.

(Fig 3) SISO and MIMO data transmission


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1) For PHY enhancement:

In the concept of SISO the effectiveness of data transfer is limited by multipath interferences

occurring between transmitter antenna and receiver antenna which are mostly subject of been

out of synchronization, as client devices can be moved from “hot spot” to “cold spot”. In the

contrary of the MIMO concept the transmitter and receiver take advantage of data transfer

multiple paths; they are therefore less subject of multipath interference. Applying the MIMO

system on 802.11 WLAN, helps increase the speed of its throughput. Also MIMO system can

be enhanced by doubling the channel width from 20 MHz channels to 40 MHz channels

called channel bonding (Fig 4) and in other hand applying a “Beam forming” using energy

“focused” or “directed” enabling Access Point (AP) antenna array to focus the energy in the

direction of client device (Fig 5). The “beam forming” process allows increase of the Signal

to Noise Ratio (SNR), determine by the power signal over the power of noise evaluated in

Decibel (dB), at the receiver and therefore a high speed of data transfer by increasing the

power signal.

(Fig 4) Channel Bonding

(Fig 5) Process of “beam forming”


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(Fig 6) Increase in 802.11 standards and 802.11n throughput rate.

2) For MAC enhancement:

“In the 802.11b network the latency of 10 μs Short Interframe Space (SIFS) is about 14 bytes.

The same latency transfer to a moderate 802.11n will give a SIFS of over a kilobyte” (Ref 6).

The SIFS is use to dissociate the response frame from the frame soliciting the response, in

other terms it allows to dissociate the data frame from the acknowledgement (ACK) response.

In the process of SIFS the MAC is processing the time of the received frame by building a

response (Fig 7). To reduce effectively the MAC processing time, the 802.11n MAC

enhancements apply a frame aggregation technique.

(Fig 7) PHY and MAC latency generating a response frame


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The MAC aggregation residing on top and bottom of the MAC describe as (Fig 8):

- At the top of the MAC is the MAC Service Data Unit (MSDU) aggregation (or A-MSDU), which in the egress direction aggregates is the first step in forming an

MAC Protocol Data Unit (MPDU).

- At the bottom of the MAC is MPDU aggregation (or A-MPDU), which in the egress direction aggregates multiple MPDUs to form the Protocol Service Data Unit that is

passed to the PHY to form the payload of single transmission

The process consists of eliminating (Fig 9) the inter-frame space and preamble altogether and

combine data frames in a single transmission. “With this process, the throughput of 100Mbps

at the top of MAC, target set in 802.11n is easily reached” (Ref 7). MAC aggregation can

improve data transfer rate efficiency from 50% to about 75% Therefore it is an effective

throughput enhancing feature introduced in the 802.11n MAC.

(Fig 8) MAC aggregation function

(Fig 9) Basic throughput enhancements to the 802.11’s MAC.


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2.3 Features overview of IEEE 802.11n

The following are IEEE 802.11n features (Ref 8):

Compatibility of 802.11n with other standards:

- 802.11n Access Points offer mixed operation in special mode in order to allow the co-existence with wireless devices base on 802.11 standards called “Legacy Client”.

- In 802.11n environment, exist a so called “Greenfield Mode” option, it allow access to all advantages of the new technology

Technical aspects of 802.11n

- The use of OFDM as modulation method allows a maximum of 52 carrier signals and the payload data rate indicates the ratio between theoretically available bandwidth and

actual bandwidth.

- The above features increase the maximum useable bandwidth of 65 Mbps for 802.11n and 54Mbps for 802.11 standards.

- MIMO technology: As explained above, is the most important improvement aspect of 802.11 standards, allowing effective increased throughput for better Quality of

Service (QoS). It allows the use of “Dual-slant” antennas which transmit two data

streams in parallel using polarization channels positioned at 90ºC to each other for

outdoor use.

- 802.11n allows short Guard interval technology: it permits a signal to be transmitted in WLAN to benefit from chronological sequence of data transmission which “held

up” data for a short constant transmission of period to avoid interference at the

receiver antennas.

Optimizing net data throughput

- Frame aggregation: Is another main improvement technology of 802.11n standard allowing effective increase throughput rate from MAC frame aggregation as described

above.

- Block acknowledgment: For some reason, one or more packet in aggregated frame are not delivered on time, in order to avoid a retransmission of an entire aggregated

frame, a separate acknowledgement is generated for every single WLAN unsuccessful

packet transfer in the aggregated frame called “block acknowledgment” and relay

back to the sender as a group for eventual retransfer to the receiver.

Advantage of IEEE 802.11n:

- Higher effective throughput: 802.11n include new mechanisms which increase available bandwidth, network base on it achieves and increased data throughput of up

to 300Mbps (in reality 120 to 130 Mbps net) but theoretically the throughput is

defined to 600 Mbps with four data streams.

- Improved wider wireless coverage: The new wireless generation is not only increasing data throughput but reducing area without reception with better signal

coverage with stability. At any given location a client connected to 802.11n AP with

MIMO will benefit from greater throughput coverage.


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- Greater range reliability: Compare to the 802.11 standards, 802.11n transmitter and receiver antennas have greater reception capability as distance between APs increases

significantly or less.

3 - Approaches and Methodology

3.1 Physical Layer (PHY) extension function

802.11n uses several PHYs extension to enhance improvement on 802.11 standards,

increasing the maximum throughput rate from 54 to 600 Mbps. To allow this function the

following method were adopted:

- 52 OFDM data subcarriers are used, in place of 48, permitting a data rate increase by a factor of 13/12 to 58.5Mbps.

- A new Forward Error Correction (FEC) coding rate of 5/6 enables 65 Mbps from the Modulation Coding Scheme (MCS)

(Fig 10) MCS parameters for mandatory 20 MHz

- Depending on the channel quality the guard interval can be reduced from 800 ns to 400 ns giving a very short duration of 3.2 µs for an increased throughput rate of

72.2Mbps.

- With the MIMO technique, transmission of multiple streams simultaneously over 4 antennas at the transmitter and receiver can be done with a single channel. The

process outcome is a throughput rate increase from 72.2 Mbps to 288.9Mbps.

- The 40 MHz channels in used, double the channel bandwidth allowing the increase of data subcarriers from 52 to 108 and the MIMO channel throughput of 150Mbps

giving 600Mbps using four antennas.


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(Fig 11) Symbols used in MCS parameter tables

3.2 Medium Access Control (MAC) extension function

802.11n support 2 types of aggregation on MAC level:

- Aggregation of MSDU at the top of the MAC called A-MSDU operation. - Aggregation of MAC Protocol Data Units located at the bottom of the MAC called A-

MPDU operation.

(Fig 12) A-MPDU and A-MSDU Aggregated Frame Formats

The MAC frame aggregation allows the amount of Protocol Control Information (PCI) of

the PHY and the access delay of the Distributed Coordination Function (DCF), MAC


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protocol using the listen-talk scheme based on Carrier Sense Multiple Access/Collision

Avoidance (CSMA/CA), per MSDU are reduced significantly since the PHY PCI and

contention/ACK transmission is only required once per all aggregated frames reducing

delays over packet transfer.

3.3 PHY system Model function The 802.11n PHY model decides which packet transmission is successful, like when packet

is decoded error-free at receiver side. It depends on three factors:

- Level of background noise and other activity transmission interference with signal - At what time the active transmission have started - Which PhyMode, in other term MCS, Nss is selected at the transmitter.

The quality of the received signal measured by the Signal to Interference plus Noise Ratio

(SINR) expressed in decibel (dB) is affected by 2 factors:

- Thermal-noise - Receiver noise (from Radio Frequency “RF” of up to 7 dB for station and 5dB for

APs)

3.4 MIMO system Model function

For every multipath component (p), the angle of arrival (AOA= ) and angle of departure

(AOD= ) are defined with the array normal of the according antenna array and the

position of dominant reflector. The direction of the transmitter array (TX-array) and the

receiver array (RX-array) with respect to the Line of Slight (LOS) are defined by respectively

and . The small time delay of the arrival of the waveform between different antennas

results in a Phase-Shift at these Receiver antennas (RX-antennas) which can be reduced

significantly with a very low Transmitter antennas (TX-antennas) carrier signal wavelength

(Ref 9).

(Fig 13) MIMO scattering function scenario


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The quality of the signals from the TX-antennas to the RX-antennas can also be improved in

the MIMO system model by using the best MIMO-Space-Time Fading type correlation

between:

- The signal received at different RX-antennas

- The signal transmitted from different TX-antennas

For a better transmitted signal from the transmitter antennas and a better signal received at

the receiver antennas, using at the appropriate correlated channels at the TX-antennas and

RX-antennas, providing the ideal MIMO channel fading type for appropriate 4-path channel

depending on the channel acknowledgment.

(Fig 14) MIMO-Fading Correlation between signals received at different RX-antennas

(Fig 15) MIMO-Fading Correlation between signals transmitted from different TX-antennas


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(Fig 16) Types of MIMO channel fading

The above MIMO channel type of fading quality in (Fig 16) is base on the amount of

knowledge the transmitter has about the channel used in each cases, which are:

- Complete channel knowledge

- Average channel knowledge

- No channel knowledge

(Fig 17) Comparison of semi-correlated and uncorrelated channels with and without channel

knowledge

4 - 802.11n performance limitations and

propositions for improvement

4.1 Limitation of the 802.11n performance

From the approach and methodology above, it comes to our critique that several dependent

criteria affect the PHY function, MAC function and the MIMO model function performance

and therefore directly or indirectly the performance of the 802.11n enhancement improving

the 802.11 standards. These criteria are as follow:

- The guard interval performance depends on the channel used quality to allow a reduced duration delay over the throughput rate.

- The noise interference at the receiver antennas (RX-antennas) affect the quality of the throughput


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- The conditions for a packet to be decoded error-free at the receiver, if not satisfied, do not allow an effective performance of the received signal.

- Conditions allowing appropriate type of correlation at the TX-antennas and RX-antennas to apply a perfect MIMO channel fading type may not be fully completed

and depend on the channel acknowledgment.

4.2 Propositions to improve 802.11n performance

The above 802.11n limitations can be overcome by:

- Increasing the maximum of channel used in MIMO system to up 8 reducing effectively the guard interval period to probably lower than 100 ns and improving the

throughput to up to a 5Gbps.

- Increasing the channel frequency from 40 MHz to up 150, improving the channel bonding process and for a better “beam forming” process allowing increase of power

signal using energy “Directed” over APs. This process will minimized the noise

interference at the receiver gaining a throughput rate of up to 5Gbps.

- Reduce the thermal-noise and receiver noise at the receiver with a lower RF and heat control system at the receiver to increase the Signal to Interference plus Noise Ratio

(SINR), therefore the quality of the received signal, and ease a rapid and efficient

throughput rate.

- To model a channel fading correlations a random channel matrix needed to be written (Ref 10) using different cases allowing implementation of respective channel type of

fading (Fig 16). To render more accurate the channel capacity, the fixed “complete

channel knowledge" option is preferred due to the uncertainty over the “average

channel knowledge” and the “no channel knowledge” options.

5 - Conclusion

Our investigation on 802.11n shows that it is a work of TGn group which permitted an

amendment of 802.11 standards, precisely the 802.11a/b/g, ratified in October 2009 and

allowing a throughput rate best quality. The improvement over 802.11 standards is mainly the

use of MIMO system compare to the SISO previously used, enhancing the PHY and MAC

approach which introduced very important features over the 802.11n compatibility with other

standards, improved its technical aspect for better QoS, optimized net data throughput

through frame aggregation and block acknowledgment technology. This enhancement gives a

higher throughput rate quality to a maximum 600 Mbps, allows wider wireless coverage, and

gives greater range reliability. Also the enhancement is being permitted mainly through the

use of 52 OFDM data subcarriers, the aggregation of MSDU and MPDU. But 802.11n

enhancement has some limitations over its performance affecting the quality of its throughput

at some points as listed above. To overcome these limitations, our propositions to improve

802.11n performance can be implemented with appropriate tools and technical support to

allow an 802.11(n) efficient throughput rate up to 5Gbps.


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6 - References

(Ref 1, Fig 12) Tom Alexander (2007) Optimizing and Testing WLANs, 30 Corporate Drive, Suite

400, Burlington, MA 01803, USA Linacre House, Jordan Hill, Oxford OX2 8DP, UK: Newnes is an

imprint of Elsevier. (Page 3)

(Ref 2) Patil, Basavaraj, et. al. IP in Wireless Networks. Upper Saddle River, NJ: Prentice Hall, 2003.

(Ref 5) IEEE Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)

Specifications – Enhancements for Higher Throughput, IEEE Amendment 802.11n-2009.

(Fig 2) Justin Berg (2010) The IEEE 802.11 standardization its history, specifications,

implementations, and future, 4400 University Drive MS#2B5: George Mason University.

(Ref 6) Matthew S. Gast (30-03-2012) 802.11n a Survival Guide, 1005 Gravenstein Highway North,

Sebastopol, CA 95472: O'Reilly Media Inc.(Page 3)

(Fig 7) Eldad Perahia and Robert Stacey (2008) Next Generation Wireless LANs, Published in the

United States of America by Cambridge University Press, New York: Cambridge University press.

(Ref 7) Eldad Perahia and Robert Stacey (2008) Next Generation Wireless LANs, Published in the

United States of America by Cambridge University Press, New York: Cambridge University

press.(Page 206)

(Ref 8) The Hirschmann (01/06/10) IEEE 802.11n Overview, White Paper edn., Hirschmann

Automation and Control GmbH Stuttgarter Str. 45-51 72654 Neckartenzlingen Germany: Cambridge

University press.

(Fig 10, 11) The 802.11 Working Group of the 802 Committee (June 2009) Wireless LAN Medium

Access Control (MAC) and Physical Layer (PHY) specifications, IEEE Standards Draft edn., Three

Park Avenue New York, NY 10016-5997, USA: IEEE P802.11n™/D11.0.

802.11 Timelines

http://www.ieee802.org/11/Reports/802.11_Timelines.htm

http://telecom.gmu.edu/sites/default/files/publications/Berg_802.11_GMU-TCOM-TR-8.pdf

IEEE 802.11

http://en.wikipedia.org/w/index.php?title=IEEE_802.11&action=edit&section=9

(Ref 3) 802.11n: Next-Generation Wireless LAN Technology

http://www.broadcom.com/collateral/wp/802_11n-WP100-R.pdf

(Ref 4) Wireless Fidelity (Wi-Fi)

http://www.techopedia.com/definition/10035/wireless-fidelity-wi-fi

http://www.ieee802.org/11/Reports/802.11_Timelines.htmhttp://telecom.gmu.edu/sites/default/files/publications/Berg_802.11_GMU-TCOM-TR-8.pdfhttp://en.wikipedia.org/w/index.php?title=IEEE_802.11&action=edit&section=9http://www.broadcom.com/collateral/wp/802_11n-WP100-R.pdfhttp://www.techopedia.com/definition/10035/wireless-fidelity-wi-fi


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(Fig 4) Channel Bonding

http://eprints.usq.edu.au/8454/1/Chan_2009.pdf

(Fig 5) IEEE 802.11n advantage

http://redpinesignals.com/pdfs/Why11n.pdf

(Fig 10) IEEE P802.11n™/D11.0

http://www.iith.ac.in/~tbr/teaching/docs/802.11n-DraftStd_June2009.pdf

Wi-Fi who we are

http://www.wi-fi.org/who-we-are

(Fig 13, 14, 15 and Ref 9) MIMO system Model function

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.14.9313&rep=rep1&type=pdf

(Fig 16, 17 and Ref 10) Correlated Fading in MIMO-Systems

http://wr.lib.tsinghua.edu.cn/sites/default/files/1116570943296.pdf
http://eprints.usq.edu.au/8454/1/Chan_2009.pdfhttp://redpinesignals.com/pdfs/Why11n.pdfhttp://www.iith.ac.in/~tbr/teaching/docs/802.11n-DraftStd_June2009.pdfhttp://www.wi-fi.org/who-we-arehttp://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.14.9313&rep=rep1&type=pdfhttp://wr.lib.tsinghua.edu.cn/sites/default/files/1116570943296.pdf

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