80211a BER and PER Performance

Introduction

WLAN_80211a_PER_prj design examples are described in this chapter.

When baseband simulation is performed, the signal power per bit can be calculated:

where Ps = received signal power, T FFT = IFFT/FFT period (3.2 µ in IEEE802.11a), T SYM = one OFDM symbol interval (4.0 µ in IEEE802.11a), N DBPS = number of data bits per OFDM symbol (refer to Table 78 in IEEE802.11a specification). The relation between N DBPS and T SYM is

where Rb = data rate.
Eb can be calculated:

The noise power per bit can be calculated:

where T s is the sample rate.
So, Eb/N0 can be calculated:

And noise variance
is

When RF simulation is performed, noise density is modeled using the AddNDensity component. According to the defining equation for parameter NDensity:

So, in WLAN_80211a_PER_prj, NDensity can be calculated:

BER and PER Performance, AWGN Channel 24 Mbps WLAN_80211a_24Mbps_AWGN_System.dsn

Features

Description

This design shows system performance with 24 Mbps data rate and channel coding under AWGN. A burst length of 1000 bytes is simulated.

The top-level schematic is shown in the following figure. This design contains four subnetworks named SignalSource, Noise, Receiver, and BERPER.

WLAN_80211a_24Mbps_AWGN_System.dsn Schematic

SignalSource parameters are contained in Signal_Generation_VARs; Noise, Receiver, and BERPER parameters are contained in RF_Channel_Measurement_VARs.

The SignalSource subnetwork (see the following figure) generates an IEEE 802.11a signal source based on user settings.

WLAN_80211a_RF Schematic

The Receiver subnetwork (see the following figure) receives an IEEE 802.11a RF signal and demodulates the signal as bits stream; it also detects the start of frame and the transition from short sequences to channel estimation sequences, estimates complex channel response coefficients for each subcarrier, transforms the symbol into subcarrier received values; it performs phase estimation from the pilot subcarrier, subcarrier derotation according to the estimated phase, and division of each subcarrier value with a complex estimated channel response coefficient.

WLAN_80211a_RF_RxFSync.dsn Schematic

The BERPER subnetwork (see the following figure) measures system BER and PER.


WLAN_80211a_BERPER Schematic

Simulation Results

Simulation results displayed in WLAN_80211a_24Mbps_AWGN_System.dds are shown in the following figure.

For PER performance, it shows that WLAN_80211a_24Mbps_AWGN_System.dsn is approximately 0.5 dB better than that of Richard van Nee's text book (page 251 in [2]).

Reference data points are shown in page Equations.

WLAN_80211a_24Mbps_AWGN_System Simulation Results

Benchmark

References
  1. IEEE Standard 802.11a-1999, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5 GHz Band," 1999.
  2. Richard van Nee, Ramjee Prasad, OFDM Wireless Multimedia Communications, Artech House, 2000.

BER and PER Performance, Phase Noise Distortion 24 Mbps

WLAN_80211a_24Mbps_PN_System.dsn

Features

Description

This design demonstrates system performance with 24 Mbps data rate and channel coding under phase noise distortion. A burst length of 128 bytes is simulated.

The power density spectrum of an oscillator signal with phase noise is modeled by a Lorentzian spectrum. The single-sided spectrum S s (f) is given by

The following figure illustrates a Lorentzian phase noise spectrum with a single-sided -3 dB line width of the oscillator signal. The slope per decade is -20 dB.

Phase Noise Power Spectral Density (PSD)

In this phase noise distortion test, two cases of phase noise are used to measure PER/BER. The -3 dB line width of phase noise 1 is 30.0 Hz (=0.01% of subcarrier space of IEEE 802.11a); the -3 dB line width of phase noise 2 is 3.0 Hz (=0.001% of subcarrier space of IEEE 802.11a). And, an Ideal test case (no phase noise) is used as a reference.

The schematic for this design is shown in the following figure.

WLAN_80211a_24Mbps_PN_System.dsn Schematic

N_Tones is used to model the phase noise. The following figure shows the N_Tones parameters and phase noise test cases of the oscillator used in this design. A variable AA is used to control the case of phase noise.

N_Tones Parameters

Ideal, phase noise 1, and phase noise 2 results are shown in the following three figures.

Spectrum of Ideal Case

Spectrum of Phase Noise 1

Spectrum of Phase Noise 2

Simulation Results

Simulation results displayed in WLAN_80211a_24Mbps_PN_System.dds are shown in the following figure for BER and PER.

The BER performance of 3Hz -3dB line width is almost the same as that of no phase noise case (Ideal); the BER performance of 30 Hz -3dB line width is much poorer than those of 3Hz -3dB line width and no phase noise case.

The PER performance of 3Hz -3dB line width is a little gain lose than that of no phase noise case (Ideal); the PER performance of 30 Hz -3dB line width is much poorer than those of 3Hz -3dB line width and no phase noise case. In fact, frequency synchronization, phase tracking, and channel estimation functions, and so on, in the IEEE 802.11a receiver will cause phase noise. The phase noise of 3Hz -3dB line width is not very serious. So, its BER and PER performances are almost the same as those of Ideal case because the receiver will cause phase noise which is reasonable. For 30Hz -3dB line width, it causes serious phase noise; BER and PER performances are very poor.

BER and PER Results for 3 Test Cases

Benchmark

References
  1. IEEE Standard 802.11a-1999, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5 GHz Band," 1999.
  2. Richard van Nee, Ramjee Prasad, OFDM Wireless Multimedia Communications, Artech House, 2000.

BER and PER Performance, Fading Channel 24 Mbps

WLAN_80211a_24Mbps_Fading_System.dsn

Features

Description

This design shows system performance with 24 Mbps data rate and channel coding under fading channel. A burst length of 512 bytes is simulated.

The top-level schematic for this design is shown in the following figure.

SignalSource parameters are contained in Signal_Generation_VARs; Receiver, and BERPER parameters are contained in RF_Channel_Measurement_VARs.

WLAN_80211a_24Mbps_Fading_System.dsn Schematic

According to reference 2, five model types have been designed. Model A, an 18-tap fading channel corresponding to a typical office environment for NLOS conditions and 50ns average rms delay spread, is selected in this example. In order to reduce the number of taps needed, the time spacing is non-uniform; for shorter delays, a more dense spacing is used. The average power declines exponentially with time. For model A all taps have Rayleigh statistics. The characteristics of this model are shown in the following table.

Model A Characteristics
Tap Number Delay(ns) Average Relative Power (dB) Ricean K Doppler Spectrum
1 0 0.0 0 Class
2 10 -0.9 0 Class
3 20 -1.7 0 Class
4 30 -2.6 0 Class
5 40 -3.5 0 Class
6 50 -4.3 0 Class
7 60 -5.2 0 Class
8 70 -6.1 0 Class
9 80 -6.9 0 Class
10 90 -7.8 0 Class
11 110 -4.7 0 Class
12 140 -7.3 0 Class
13 170 -9.9 0 Class
14 200 -12.5 0 Class
15 240 -13.7 0 Class
16 290 -18.0 0 Class
17 340 -22.4 0 Class
18 390 -26.7 0 Class

Simulation Results

Simulation results displayed in WLAN_80211a_24Mbps_Fading_System.dds are shown in the following two figures.

For PER performance, it shows that WLAN_80211a_24Mbps_Fading_System.dsn is approximately 2 dB better than that of WLAN_80211a_36Mbps_Fading_System.dsn.

802.11a Fading Channel BER Performance

802.11a Fading Channel PER Performance

Benchmark

References
  1. IEEE Standard 802.11a-1999, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5 GHz Band," 1999.
  2. Channel Models for HIPERLAN/2 in Different Indoor Scenarios, ETSI EP BRAN 3ER1085B 30 March 1998.

BER Performance, AWGN Channel 16-QAM Modulation

WLAN_80211a_36Mbps_AWGN_Perfect.dsn

Features

Description

This design shows raw BER performance under AWGN channel with perfect channel estimator. In this design, the data rate is 36 Mbps; the raw data rate is 48 Mbps because there is no channel coding. The guard interval ratio is 1/4 and modulation mode is 16-QAM. The number of frames is set according to Eb/No.

Schematic

The top-level schematic for this design is shown in the following figure.

WLAN_80211a_36Mbps_AWGN_Perfect Schematic

The SignalSource subnetwork (see the following figure), multiplexes short and long preambles, one signal symbol and data OFDM symbols into a burst frame.

WLAN_80211a_RF Schematic

The sub_WLAN_Rx_RF_AWGN_Perfect.dsn subnetwork (see the following figure) performs the start of frame and the transition from short to channel estimation sequences detections, establishment of fine timing (with one sample resolution), and division of each subcarrier value with an ideal channel response coefficient.

sub_WLAN_Rx_RF_AWGN_Perfect Schematic

The BERPER subnetwork (see the following figure) measures system BER and PER.

WLAN_80211a_BERPER Schematic

Notes

Order can be set to 6, 7 or 8 in Signal_Generation_VARs.

Simulation Results

The following figure shows Gaussian channel BER of different Eb/N0.

Raw BER Measurements

The red curve, which represents the symbol error rate from Figure 5-2-16 [2], is converted using a dividing factor of 4 into the bit error rate of this design; for 16-QAM modulation, n b =4. The blue curve shows the BER of this design. The difference in the two curves is less than 0.2 dB. The WLAN Design Library simulation result is consistent with the theoretical result.

To convert symbol error rate into bit error rate, ps is the probability of a symbol error, pb is the probability of a bit error. The relation between ps and p b is

where nb = number of bits per symbol. Assuming the modulation signal is Gray coded, p b <<1,
then,

So,

Benchmark

References
  1. IEEE Standard 802.11a-1999, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5 GHz Band," 1999.
  2. John G. Proakis, Digital Communications, third edition, McGraw-Hill, Inc. 1995.

BER and PER Performance, AWGN Channel 36 Mbps

Design Name

WLAN_80211a_36Mbps_AWGN_System.dsn

Features

Description

This design shows BER and PER performance with 36 Mbps data rate and channel coding under AWGN. Burst lengths of 128, 256, and 512 bytes are simulated.

The top-level schematic is shown in the following figure. This design contains four subnetworks named SignalSource, Noise, Receiver, and BERPER.

WLAN_80211a_36Mbps_AWGN_System Schematic

SignalSource parameters are contained in Signal_Generation_VARs; Noise, Receiver, and BERPER parameters are contained in RF_Channel_Measurement_VARs.

The SignalSource subnetwork (see the following figure) generates an IEEE 802.11a signal source based on user settings.

WLAN_80211a_RF Schematic

The Receiver subnetwork (see the following figure) receives an IEEE 802.11a RF signal and demodulates the signal as bits stream; it also detects the start of frame and the transition from short sequences to channel estimation sequences, estimates complex channel response coefficients for each subcarrier, transforms the symbol into subcarrier received values; it performs phase estimation from the pilot subcarrier, subcarrier derotation according to the estimated phase, and division of each subcarrier value with a complex estimated channel response coefficient.

WLAN_80211a_RF_RxFSync Schematic

The BERPER subnetwork (see the following figure) measures system BER and PER.

WLAN_80211a_BERPER Schematic

Simulation Results

Simulation results displayed in WLAN_80211a_36Mbps_AWGN_System.dds are shown in the following figure.

WLAN_80211a_36Mbps_AWGN_System Simulation Results

For BER performance, when Eb/N0 is above 10dB, the curve for the 128-byte burst is slightly different from the 256-byte burst and the 512-byte burst curves; this is because the bit number of the 128-byte curve is approximately 10 million fewer than the 256-byte and the 512-byte curves, which are approximately 20 and 40 million bits, respectively. We can conclude that the BER performance for different burst lengths are the same when enough test bits are used.

For PER performance, it shows that the performance of the 128-byte curve is better than that of the 256-byte curve, which is better than that of 512-byte curve. We can conclude that the longer the burst length the worse the PER performance.

Benchmark

References
  1. IEEE Standard 802.11a-1999, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5 GHz Band," 1999.
  2. John G. Proakis, Digital Communications, third edition, McGraw-Hill, Inc. 1995.

BER Performance, AWGN Channel 64-QAM Modulation

WLAN_80211a_48Mbps_AWGN_Perfect.dsn

Features

Description

This design shows raw BER performance under AWGN channel with perfect channel estimator. In this design, the data rate is 48 Mbps; the raw data rate is 72 Mbps because there is not channel coding. The guard interval ratio is 1/4 and modulation mode is 64-QAM.

The top-level schematic for this design is shown in the following figure.

WLAN_80211a_48Mbps_AWGN Schematic

The SignalSource subnetwork (see the following figure) generates an IEEE 802.11a signal source based on user settings.

WLAN_80211a_RF Schematic

The sub_WLAN_Receiver_AWGN_Perfect subnetwork (see the following figure) detects the start of frame and the transition from short sequences to channel estimation sequences, establishes fine timing (with one sample resolution), and divides each subcarrier value with an ideal channel response coefficient.

sub_WLAN_Rx_RF_AWGN_Perfect Schematic

The BERPER subnetwork (see the following figure) measures system BER and PER.

WLAN_80211a_BERPER Schematic

Notes

Order in Signal_Generation_VARs can be set to 6, 7 or 8.

Simulation Results

Simulation results are shown in the following figure.

Gaussian Channel BER of Different Eb/N0

The red curve, calculated from Figure 5-2-16 [2], shows the symbol error rate. The symbol error rate is converted into the bit error rate; ps is the probability of a symbol error, pb is the probability of a bit error. The relation between ps and p b is

where nb = number of bits per symbol. Assuming the modulation signal is Gray coded, p b <<1, then

So,

In this design, the modulation is 64-QAM, nb=6, the red curve was converted from [2] using a dividing factor of 6; the blue curve shows the BER of this design and the difference is less than 0.4 dB. Simulation results of this design are consistent with the theoretical results.

Benchmark

References
  1. IEEE Standard 802.11a-1999, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5 GHz Band," 1999.
  2. John G. Proakis, Digital Communications, third edition, McGraw-Hill, Inc. 1995.

BER and PER Performance,

Fading Channel 36 Mbps
WLAN_80211a_36Mbps_Fading_System.dsn

Features

Description

This design shows system performance with 36 Mbps data rate and channel coding under fading channel. A burst length of 512 bytes is simulated.

The top-level schematic for this design is shown in the following figure. SignalSource parameters are contained in Signal_Generation_VARs; Noise, Receiver, and BERPER parameters are contained in RF_Channel_Measurement_VARs.

WLAN_80211a_36Mbps_Fading_System.dsn Schematic

According to reference 2, five model types have been designed. Model A, an 18-tap fading channel corresponding to a typical office environment for NLOS conditions and a 50ns average rms delay spread, is used in this example. In order to reduce the number of taps needed, the time spacing is non-uniform; for shorter delays, a more dense spacing is used. The average power declines exponentially with time. For Model A, all taps have Rayleigh statistics. The characteristics of this model are listed in the following table.

Model A Characteristics
Tap Number Delay (ns) Average Relative Power (dB) Ricean K Doppler Spectrum
1 0 0.0 0 Class
2 10 -0.9 0 Class
3 20 -1.7 0 Class
4 30 -2.6 0 Class
5 40 -3.5 0 Class
6 50 -4.3 0 Class
7 60 -5.2 0 Class
8 70 -6.1 0 Class
9 80 -6.9 0 Class
10 90 -7.8 0 Class
11 110 -4.7 0 Class
12 140 -7.3 0 Class
13 170 -9.9 0 Class
14 200 -12.5 0 Class
15 240 -13.7 0 Class
16 290 -18.0 0 Class
17 340 -22.4 0 Class
18 390 -26.7 0 Class

Simulation Results

Simulation results displayed in WLAN_80211a_36Mbps_Fading_System.dds are shown in the following two figures.

For PER performance, the WLAN_80211a_36Mbps_Fading_System.dsn is approximately 2 dB worse than that of WLAN_80211a_24Mbps_Fading_System.dsn.

802.11a Fading Channel BER Performance

802.11a Fading Channel PER Performance

Benchmark

References
  1. IEEE Standard 802.11a-1999, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5 GHz Band," 1999.
  2. Channel Models for HIPERLAN/2 in Different Indoor Scenarios, ETSI EP BRAN 3ER1085B 30 March 1998.
 

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