SOFTWARE IMPLEMENTATION OF IEEE 802.11B
WIRELESS LAN STANDARD
Suyog D. Deshpande
(Sr. MTS: HelloSoft, Inc, San Jo, CA, USA; )
ABSTRACT
Software-Defined Radio (SDR) is a rapidly evolving technology that is receiving enormous recognition and generating widespread interest in the telecommunication industry. Over the last few years, analog radio systems are being replaced by digital radio systems for various applications in military, civilian and commercial areas. In addition to this, programmable hardware modules and high performance Digital Signal Processors (DSPs) are increasingly being ud in digital radio systems at different functional levels. SDR technology facilitates implementation of some of the functional modules in a radio system such as modulation/demodulation, coding, signal generation, and link-layer protocols in software. This helps in building reconfigurable software radio systems where dynamic lection of parameters for each of the above-mentioned functional modules is possible. A complete hardware bad radio system has limited utility since parameters for each of the functional modules are fixed. A
radio system built using SDR technology extends the utility
of the system for a wide range of applications that u
different protocols and modulation/demodulation
techniques.
In this paper, we discuss the software implementation
details of IEEE 802.11b Wireless LAN (WLAN) standard
on Texas Instruments’ TMS320C6416 DSP bad hardware
platform.
1. INTRODUCTION
The term Software-Defined Radio refers to the u of
software-programmable hardware to provide flexible radio
solutions. The concept behind the technology is that it will台州中学
provide software control of radio functionality. Traditional
radio designs are constructed of fixed analog or digital
components. Such designs also are custom built for each
application. By comparison, SDR technology offers an
inherent flexibility and rves as the main incentive to
engage in this methodology.
SDR is a rapidly evolving technology that is receiving
enormous recognition and generating widespread interest in
the telecommunication industry. It has generated
tremendous interest in wireless communication industry for
its wide range economic and deployment benefits. It
facilitates implementation of some of the functional modules in a radio system such as modulation/demodulation, coding, signal generation, and link-layer protocols in software. This helps in building reconfigurable software radio systems where dynamic lection of parameters for each of the above-mentioned functional modules is possible. It can be ud to implement a wide range of radio applications like WLAN, Bluetooth, and Cellular wireless (GSM, GPRS, CDMA, and UMTS) standards. In this paper, we discuss the software implementation details of IEEE 802.11b WLAN standard on Texas Instruments’ TMS320C6416 DSP bad hardware platform. The problem associated with the physical layer (PHY) of 802.11b standard is that it requires very high computational
power. One way to achieve this efficiency is by implementing the PHY completely in hardware. Introduction of high performance DSPs and our IP rich
PHY algorithms [1] have made it possible to run the entire
802.11b PHY on a single DSP. The 802.11b Medium
Access Control (MAC) layer software (including WEP
encryption) runs on the ARM core. This software
implementation approach provides ea of design
modifications at any stage of the product cycle and also in
the field even after deploying the solution. It also facilitates
addition of new features into the deployed solution with
minimal changes in the software architecture. Most
importantly it gives great deal of flexibility to make custom中国插画
changes at both PHY and MAC layers, for curity related
applications in military, civilian and commercial areas.木瓜应该怎么吃
The important aspects of SDR technology and its salient
features are prented in ction 2. A brief description about
current WLAN standards that are widely ud in
毕业论文答辩自述
肠胃炎什么症状commercial, home, office, and industrial applications is
given in Section 3. Section 4 describes the software
implementation details of IEEE 802.11b WLAN standard
on Texas Instruments’ TMS320C6416 DSP bad hardware
platform. Finally, the concluding remarks are prented in
ction 5.
2. SOFTWARE DEFINED RADIO TECHNOLOGY
SDR technology is defined as "radios that provide software control of a variety of modulation techniques, wide-band or narrow-band operation, communications curity functions (such as hopping), and waveform requirements of current & evolving standards over a broad frequency range.” [2]
SDR has generated tremendous interest in the wireless communication industry for the wide range economic and deployment benefits it offers for military, civilian and commercial applications. The momentum of SDR in defen applications has been spearheaded by the United States Government's JTRS program. The program requirement calls for "affordable, high-capacity tactical radios that meet the bandwidth needs of various echelons. Therefore, a software-programmable and hardware-configurable digital radio system is required to provide incread interoperability, flexibility, and adaptability to support the varied mission requirements of the war fighters". Some of the key features of SDR technology are
Co-existence and Dynamic Configurability: SDR allows co-existence of multiple software modules implementing different standards on the same system allowing dynamic configuration of the system by just lecting the appropriate software module to run. It facilitates implementation of future-proof, multi-rvice, multi-mode, multi-band, multi-standard terminals and infrastructure equipment. Connectivity: SDR enables implementation of air interface standards as software modules and multiple instances of such modules that implement different standards can co-exist in infrastructure equipment and handts. This helps in realizing global roaming facility.
One of the major incentives for using the SDR technology is to overcome the problems faced by the
wireless communication industry due to implementation of wireless networking infrastructure equipment and terminals completely in hardware.
Commercial wireless network standards are continuously evolving from 2G to 3G and then further onto 4G. Each generation of networks differ significantly in link-layer protocol standards causing problems to subscribers, wireless network operators and equipment vendors. The air interface and link-layer protocols differ across various standards like WLAN, Bluetooth, GSM, GPRS, CDMA, and UMTS. This problem has inhibited the deployment of global roaming facilities causing great inconvenience to subscribers who travel frequently from one continent to another. Subscribers are forced to buy new handts whenever a new generation of network standards is deployed. Wireless network operators face problems during migration of the network from one generation to next due to prence of large number of subscribers using legacy handts that may be incompatible with newer generation network.
Handt vendors face problems in building viable multi-mode handts due to high cost and bulky nature of such handts. The network operators also need to incur high equipment costs when migrating from one generation to next. They also face deployment issues while rolling-out new rvices/features to realize new revenue-streams since this may require large-scale customizations
on subscribers’ handts. Equipment vendors face problems in rolling out newer generation equipment due to short time-to-market requirements.
SDR technology enables implementation of radio functions in networking infrastructure equipment and subscriber terminals as software modules running on a generic hardware platform. This significantly eas migration of networks from one generation to another since the migration would involve only a software upgrade. Further, since the radio functions are implemented as software modules, multiple software modules that implement different standards can co-exist in the equipment and handts. An appropriate software module can be chon to run (either explicitly by the ur or implicitly by the network) depending on the network requirements. This helps in building multi-mode handts and equipment resulting in ubiquitous connectivity irrespective of underlying network technology ud.
However, SDR technology has some drawbacks like higher power consumption, higher processing power (MIPS) requirement and higher initial costs. SDR technology may not be suitable for all kinds of radio equipment due to the factors. , SDR technology may not be appropriate in pagers while it may offer great benefits when ud to implement ba-stations. Hence the factors should be carefully considered before using SDR technology in place of a complete hardware solution.
3. IEEE 802.11 WLAN STANDARDS Currently, three WLAN standards are in wide commercial, home, office, and industrial u: 802.11a, 802.11b, and the recently IEEE-ratified 802.11g. Several chip manufacturers are building chipts that work with both 11b and 11g, and a smaller number are building a chip capable of working on both 11a and 11g or with 11a, 11b, and 11g.
802.11b products, available since 1999, operate in the unlicend 2.4-gigahertz (GHz) ISM (Industrial Scientific and Medical) radio spectrum; support average data rates of 1, 2, and 5.5 megabits per cond (Mbits/s); and can achieve a maximum of 11 Mbits/s [3].
802.11a products, available since 2002, operate in unlicend portions of the 5-GHz radio spectrum, with maximum achievable data rates up to 54 Mbits/s [4].
802.11g products operate in the same 2.4-GHz radio spectrum that 802.11b products operate in and therefore provide backward compatibility with them, but their higher data rates remble tho of 802.11a products. The IEEE ratified the 802.11g standard [5] on 12 June 2003 after three years of working-group deliberations. 11g will now undergo a lengthy period of testing and certification, even though 11g-enabled products are already flooding the market.
The frequency band in u constitutes one key difference among the three standards. The 11b an
d 11g standards both u the 2.4-to-2.4835-GHz band, and each runs on 3 channels only; 11a, which us the 5.725-to-5.850-GHz band, is currently capable of operating with up to 12 channels. This capability potentially makes 802.11a valuable for large-scale enterpri installations: More transmission channels in 11a also support a higher density of urs per access point in a given space than either 11b or 11g supports. Becau 11a us a frequency band different from that of 11b and 11g, 11a is not backward compatible with either 11b or 11g.
Data rate constitutes another key difference among the three standards: The 11b standard provides a much lower data-throughput performance than do the 11a and 11g standards. Implementations of 11a and 11g provide up to a maximum best data level of 54 Mbits/s; 11b is limited to 11 Mbits/s. In other words, 11a and 11g transfer data roughly five times faster than does 11b. However, actual data rates of data communications networks are lower than nominal maximum rates becau of packet overhead. And wireless packet networks suffer from interference, which further erodes actual data rates.
Different wireless LAN standards also rely on different modulation techniques and the implementation complexity depends on the modulation scheme being ud. Both 11a and 11g products rely on orthogonal frequency-division multiplexing (OFDM). OFDM is what gives the two sta
ndards a higher throughput than that of 802.11b, which us the less-efficient direct-quence spread-spectrum (DSSS) method.
Since full software implementation of 11a or 11g PHY layers is not realizable, our discussion will be focud on implementation details of 11b PHY only.
4. 802.11B IMPLEMENATION DETAILS
This ction describes the software implementation aspects of IEEE 802.11b WLAN standard on Texas Instruments’ TMS320C6416 DSP bad hardware platform. The problem associated with 802.11b PHY is that it requires very high computational power. One way to achieve this efficiency is implementing it completely in hardware. Almost all standard 11b chipts implement 11b PHY in hardware. The MAC is implemented as a combination of hardware and software. This is very efficient implementation in terms of power consumption and die size area. But this implementation does not provide any flexibility in making custom changes to both PHY and MAC layers.
Our IP rich PHY algorithms in conjunction with high performance DSPs have made it possible to run the entire 802.11b PHY on a single TMS320C6416 DSP. The 802.11b MAC software including WEP encryption runs on the ARM core. This software implementation approach provides ea of design m
odifications at any stage of the product cycle and also in the field even after deploying the solution. It also facilitates addition of new features into the deployed solution with minimal changes in the software architecture. Most importantly it gives great deal of flexibility to make custom changes at both PHY and MAC levels, for curity related applications in military, civilian and commercial areas.
To establish the proof of concept and demonstrate interoperability of the 802.11b technology, we have developed a reference board centered on TI TMS320C6416 and ALTERA’s Excalibur FPGA chip. A brief block diagram of the reference board is shown below.
Figure 1: WLAN Reference Design Block Diagram
The IP rich PHY algorithms and optimized implementation on TMS320C6416 has made is possible to run the entire IEEE 802.11b PHY on a single TMS320C6416 DSP chip running at 600 MHz (without using any of the available co-processor engines). The 802.11b MAC including WEP encryption runs on the ARM core that is prent inside the Excalibur. Communication between the MAC and PHY as well as the communication between the RF Front end and PHY is aided by the glue logic implemented on the Excalibur FPGA.
The transmitter architecture for 1 & 2 Mbps is shown in Figure 2. The bit stream received from the MAC is pasd through 32-bit CRC and Scrambler. Scrambler whitens the incoming bit stream. The whitened bits are differentially encoded using DBPSK or DQPSK modulation schemes. The resulting symbol is spread using 11 chip Barker quence. The Barker spreaded symbol is up sampled by a factor of 2 and given to 8-bit DACs operating at 22 MHz.
Figure 2: Block Diagram for 1 & 2 Mbps Transmitter The transmitter architecture for 5.5 & 11 Mbps transmitter is shown in Figure 3. It is same as that of 2 Mbps data rate with the only difference in the spreading quence. It is a complex quence of length 8 (CCK code). For 5.5 Mbps data rate, 2 bits are ud to lect one of 4 CCK codes where as for 11 Mbps data rate, 6 bits lect one of 64
possible CCK codes.
Figure 3: Block Diagram for 5.5 & 11 Mbps Transmitter The receiver architecture for 1 & 2 Mbps data rates with Barker despreading is shown in Figure 4. The signal received from the receive antenna is down converted from RF to Baband. The analog I and Q samples are fed to 8-bit ADCs operating at 22 MHz. The RAKE engine combines up to 8 paths at 22 MHz in a very efficient way to enhance the receiver performance. Decision Feedback Equalizer (DFE) is also included in the receiver to minimize the effect of inter-symbol-interference (ISI) thereby reducing the packet error rate (PER).
Figure 4: Block Diagram for 1 & 2 Mbps Receiver
九字开头成语The receiver architecture for 5.5 & 11 Mbps data rates with CCK despreading is given in Figure 5. Matched filter interpolator modules rves the purpo of matched filtering and interpolating the chip
sampling instant to generate output at 11 MHz rate. An efficient implementation of the correlation banks, which significantly reduces the computational complexity, is through Fast Walsh Transform
(FWT) algorithm.
Figure 5: Block Diagram for 5.5 & 11 Mbps Receiver
The cycle count requirements for data mode receiver modules are given in Table 1.
Module name
Cycles 1& 2 Mbps
Cycles 5.5 Mbps Cycles 11 Mbps Rotor 065 55 55 CMF 155 90 90 FWT + BP - 70 115
De-Spreader 025 - - Dqpsk Demod 025 25 25 Symbol Decision
- 20 20 DFE 015 25 25 CRC 015 15 15 De-Scrambler 010 10 10 Fsm + Overheads
090 70 70 Total 400/600 380/436 425/436 Table 1: Cycle Count for Data Mode Receiver Modules IEEE 802.11b PHY is completely implemented in TMS320C6416 running at 600 MHz and is arguabl
y the world’s first single DSP solution. Given the very short symbol time of 11b PHY (1 micro-c for 1 & 2 Mbps and 727 nano-c for 5.5 and 11 Mbps), the challenge is to fit the entire computationally complex algorithms in real-time. The C6000 family of TI with the VelociTI architecture and our IP rich physical layer algorithms address the demands of this high processing requirement. At clock rate of 600 MHz, the TMS320C6416 DSP can process information at a rate of 4800 MIPS. In addition to clock rate, more work can be done each cycle with the VelociTI.2 extensions to the VelociTI architecture allowing a maximum of 8 instructions per clock cycle. The extensions include new instructions to accelerate performance in key applications and extend the
parallelism of the architecture. The complete code is written with a mix of ANSI C and asmbly coding. Real-time critical modules are hand-coded in asmbly and the non real-time modules are in 16-bit fixed point ANSI C. Although, TMS320C6416 DSP provides many peripherals, we have ud only the following - EDMA to receive data in real-time from the ADC’s and transmit data to the DACs, McBSP for communication between the MAC (on the ARM Processor) and the PHY (on the C64x) and GPIO for general debugging and external interrupt generation.
The major drawbacks of this approach are higher power consumption, higher processing power (MIPS) requirement and higher costs. This approach may not be suitable for all kinds of radio equip
ment due to the factors but may offer great benefits when ud to implement ba-stations.
健康早班车5. CONCLUSIONS
In this paper, we discusd the software implementation details of IEEE 802.11b WLAN standard on Texas Instruments’ TMS320C6416 DSP bad hardware platform. This approach provides ea of design modifications at any stage of the product cycle and also in the field even after deploying the solution. It also facilitates addition of new features into the deployed solution with minimal changes in the software architecture. Most importantly it gives great deal of flexibility to make custom changes at both PHY and MAC layers, for curity related applications in military, civilian and commercial areas.
6. REFERENCES
[1] HelloSoft’s 802.11b PHY Layer – Detailed Design Document
[2] Software-Defined Radio (SDR) Forum ()
[3] Part 11: Wireless LAN Medium Access Control (MAC) and
Physical Layer (PHY) specifications: Higher-Speed Physical Layer Extension in the 2.4 GHz Band, ANSI/IEEE Std 802.11b-1999 (Supplement to ANSI/IEEE Std 802.11, 1999 Edition)
[4] Part 11: Wireless LAN Medium Access Control (MAC) and
Physical Layer (PHY) specifications High-speed Physical Layer in the 5 GHz Band, ANSI/IEEE Std 802.11a-1999 (Supplement to ANSI/IEEE Std 802.11, 1999 Edition)
[5] Part 11: Wireless LAN Medium Access Control (MAC) and
Physical Layer (PHY) specifications Amendment 4: Further Higher Data Rate Extension in the 2.4 GHz Band, ANSI/IEEE Std 802.11g-2003
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