04-06-2012, 01:15 PM
WIMAX OFDM ADAPTIVE MODULATION WITH BROADBAND WIRELESS TECHNOLOGY HSDPA
[attachment=24136]
This paper works comprises on the analysis of IEEE 802.16 WiMAX standards and the performance analysis of its
physical layer using the OFDM adaptive modulation and it uses the concept of cyclic prefix that adds additional
bits at the transmitter end. The signal is transmitted through the channel and it is received at the receiver end, then
the receiver removes these additional bits in order to minimize the inter symbol interference, to improve the bit
error rate and to reduce the power spectrum.
An Additive white Gaussian noise (AWGN) channel model is used with Rayleigh fading to resemble the real world
scenario. The transmitter and receiver are assumed to be in fixed positions and the channel coding is not used. The
transmitted and received signals are considered to in perfect sync with each other in time and frequency. Losses
from feeder cables, joints, connectors, jumpers are not taken in consideration.
In our research work, we investigated the physical layer performance on the basis of bit error rate, signal to noise
ratio, power spectral density and error probability. These parameters are discussed in two different models. The
first model is a simple OFDM communication model without the cyclic prefix, while the second model includes
cyclic prefix.
The study reviewed scientific articles that provide in-depth knowledge that WiMAX provides increased throughput
and better protection against multi path propagation and self interference as compared to HSDPA, furthermore, in
this paper different aspects of the model were investigated and with MATLAB simulations it has been demonstrated
that lower modulation schemes provide better performance in noisy conditions. Higher modulation schemes provide
higher data rates, but encounter high BER in noisy and low SNR conditions.
Keywords:-OFDM adaptive modulation, Additive white Gaussian noise (AWGN) channel, Rayleigh fading, bit error
rate, signal to noise ratio, MATLAB simulations, HSDPA.
Introduction
WiMAX
The IEEE 802.16 standard Worldwide Interoperability for Micro Wave Access (WiMAX) is broadband wireless
technology which provides a high-speed and last mile wireless broadband services. The frequency band range
specifies 10 Ghz to 66 Ghz in the WiMAX to coverage a wide geographical area. The Wireless Metropolitan Area
Networking (WMAN) not only offers a last mile broadband services for wireless which are alternative for DSL,
cable, and T1 level in WiMAX, but also offer back haul due to higher data rates for 802.11 hot spots (Jeffrey G et
al, 2007). The main idea to bring for WiMAX is to give better solution for broadband by using wireless
infrastructure.
HSDPA
High-Speed Downlink Packet Access (HSDPA) is the 3.5 generation before 4G, which is based on UMTS third
generation network in Release 5. UMTS third generation systems, precise in Release 99 include WCDMA air
interface. High-Speed Up-link Packet Access (HSUPA) and HSDPA belong to the family High-Speed Packet
Access (HSPA). HSPA belong to the WCDMA network, which is upgrade form of 3G network (GSM World,
2009). HSDPA offers maximum output data rates of down-link speeds 3.6, 7.2 and 14.4 Mbps. As compare to
UMTS network, HSDPA provides better quality of service, spectral quality for down-link packet data rate services.
HSPA was planned to offer high data rate at non real time, but after experiment it will show the results for low data
rate application such as VOIP (Holma and Toskala, 2004). In future, Release six and seven would get better look up
for VOIP and related services result of HSDPA.
Comparison: HSDPA vs. WiMAX
HSDPA is an upgrade to the 3G UMTS network, which is primarily designed for voice and WiMAX, which is a
new technology from scratch is designed for data. Competition between the two technologies can’t be avoided at
any cost because of the fact that their primary objective tends to cross into each other; HSDPA is converging
towards data and WiMAX is moving towards voice. It’s the industry is affirmative that the performance of both the
Electronic copy available at: http://ssrnabstract=1829995
technologies won’t be much of importance while deciding which to deploy, but would be their properties which best
fit the operators requirements.
Network architecture
The 3GPP (3GPP, release 6; 3GGP TS25.308, version 5.5.0; 3GGP TS25.855, version 5.5.0) has defined the whole
architecture for the HSPA network, from the edge to the core, from the lowest layer to the highest layer. The IEEE
802-16 specifications only define WiMAX as a technology which supports only the physical and the MAC layer
(Amimo et al, 2007; Smura T, n.d.; WiMAX Forum, 2007).
OPEX and CAPEX
HSPA is just an upgrade to the previously UMTS networks, usually just a software upgrade and/or much as
changing of transceiver at the edge (RNC, Node B). Therefore, unless a new HSPA network is being installed, the
CAPEX (capital expenditure) is very low as compared to WiMAX (Furuskar A et al, 2005). WiMAX on the other
hand is a totally new technology hence operators have to build the network from scratch for which the CAPEX is
quite high for the came coverage as of an HSPA network. The OPEX (operational expenditure) on the other hand
can be treated as nearly the same for both the technologies (Amimo et al, 2007).
Performance analysis
WiMAX uses a higher bit rate modulation coding (64 QAM) then HSPA (16 QAM). 64 QAM is supported by
HSPA release7 which cannot be used simultaneously with MIMO. Release8 of HSPA supports 64 QAM
competitive with WiMAX. HSPA on the contrary has less overhead hence the peak data rate is more than WiMAX
(Anon, 2009). WiMAX beats HSPA release6 as it has better spectrum efficiency. Release7 of HSPA has
comparable spectrum efficiency as compared to WiMAX performance.
Preliminary features of HSPA release8 show better efficiency, then WiMAX (Anon, 2009). Results are similar as
presented by 3G America (3G Americas, 2006).
WiMAX deployed in higher frequencies would have additional losses in link budget as high frequencies tend to
have low range. HSPA operates in lower frequencies leading WiMAX. Still WiMAX has the flexibility to operate in
multiple frequency bands adapting according to the region’s regulations.
Technical Comparison
HSPA and WiMAX both have been designed for high-speed packet switched services. Both technologies are similar
in the case that they support dynamic link adaptation, hybrid ARQ, dynamic scheduling, multi level QoS and
support for smart antennas. Their main difference arises in their operating frequency bands, duplex schemes, and
signal format and handover mechanism (Anon, 2009).
Simulation Environment
The simulations are designed and implemented using MATLAB. Performance is evaluated by transmitting
randomly generated data stream over an AWGN channel with Rayleigh fading. The stream is then received,
demodulated and compared for errors with the theoretical model. MATLAB v7.4.0 (Release: 2007a) was used on
HP work station which was running Microsoft Windows XP professional. Simulations were done in the computer
laboratories in the Section of Teknik at Blekinge Tekniska Högskola, Karlskrona Sweden. The rand () function was
used to create a random data stream. It uses the Mersenne twister algorithm to generate random numbers. Additive
white noise channel (AWGN) model is used to characterize the noise. Rayleigh distribution is used to simulate the
multi path fading effect. Monte Carlo simulation method is used to simulate repeatedly random sampling. In this
method the simulations are repeated with new data each time, BER is calculated each time for every simulation.
Simulation Block (Insert Figure 1)
Simulation Results
The simulation results based upon the adaptive modulation technique are presented in this section. The modulation
techniques used are BPSK, QPSK, 16QAM and 64QAM. All the modulation schemes were used to simulate the real
time environment. Un-coded EbNo vs. BER plots are presented with different modulation schemes. Un-coded data
is considered the channel encoding has not been used.
OFDM simulation with adaptive modulation in AWGN
A random data stream was transmitted using adaptive modulation in an AWGN channel with Rayleigh fading using
256 OFDM pilot carriers. (Insert Figure 2) and (Insert Table 1).
Theoretical values
Theoretical values of BER are presented here for the AWGN and the Rayleigh channel for each of the modulation
schemes used.
AWGN. (Insert Figure 3) and (Insert Table 2).
Rayleigh. (Insert Figure 4) and (Insert Table 3).
Probability of error. (Insert Figure 5) and (Insert Table 4).
Theoretical vs. Actual values
Comparisons between the theoretical BER values for both AWGN and Rayleigh model with the actual values are
presented in this section for all four modulation schemes used.
BPSK. (Insert Figure 6).
QPSK. (Insert Figure 7).
16QAM. (Insert Figure 8).
64QAM. (Insert Figure 9).
Conclusion
The main concentration of this research is on the WiMAX physical layer. Performance is evaluated using an
AWGN and a Rayleigh channel which nearly resembles the real world scenarios. It has been observed that lower bit
rate modulation schemes are better in terms of power efficiency and bandwidth consumption as compared with
other modulation schemes such as QPSK, 16QAM and 64QAM. Higher modulation schemes such as 64QAM
provide high data rates, but are susceptible to higher Bit error rates (BER) on low SNR.
WiMAX adaptable modulation provides best possible error free communications in a wide range of channel
conditions, hence WiMAX provides a better throughput with its fast scheduling as compared to HSDPA. It also
provided better protection against multi path and self interference with scalable channel bandwidth and OFDMA.
The only advantage HSDPA had over WiMAX was it provided better mobility, but with the recent amendments to
the 802.16 standard, WiMAX not even supports mobility, but also supports multi hop relays.
[attachment=24136]
This paper works comprises on the analysis of IEEE 802.16 WiMAX standards and the performance analysis of its
physical layer using the OFDM adaptive modulation and it uses the concept of cyclic prefix that adds additional
bits at the transmitter end. The signal is transmitted through the channel and it is received at the receiver end, then
the receiver removes these additional bits in order to minimize the inter symbol interference, to improve the bit
error rate and to reduce the power spectrum.
An Additive white Gaussian noise (AWGN) channel model is used with Rayleigh fading to resemble the real world
scenario. The transmitter and receiver are assumed to be in fixed positions and the channel coding is not used. The
transmitted and received signals are considered to in perfect sync with each other in time and frequency. Losses
from feeder cables, joints, connectors, jumpers are not taken in consideration.
In our research work, we investigated the physical layer performance on the basis of bit error rate, signal to noise
ratio, power spectral density and error probability. These parameters are discussed in two different models. The
first model is a simple OFDM communication model without the cyclic prefix, while the second model includes
cyclic prefix.
The study reviewed scientific articles that provide in-depth knowledge that WiMAX provides increased throughput
and better protection against multi path propagation and self interference as compared to HSDPA, furthermore, in
this paper different aspects of the model were investigated and with MATLAB simulations it has been demonstrated
that lower modulation schemes provide better performance in noisy conditions. Higher modulation schemes provide
higher data rates, but encounter high BER in noisy and low SNR conditions.
Keywords:-OFDM adaptive modulation, Additive white Gaussian noise (AWGN) channel, Rayleigh fading, bit error
rate, signal to noise ratio, MATLAB simulations, HSDPA.
Introduction
WiMAX
The IEEE 802.16 standard Worldwide Interoperability for Micro Wave Access (WiMAX) is broadband wireless
technology which provides a high-speed and last mile wireless broadband services. The frequency band range
specifies 10 Ghz to 66 Ghz in the WiMAX to coverage a wide geographical area. The Wireless Metropolitan Area
Networking (WMAN) not only offers a last mile broadband services for wireless which are alternative for DSL,
cable, and T1 level in WiMAX, but also offer back haul due to higher data rates for 802.11 hot spots (Jeffrey G et
al, 2007). The main idea to bring for WiMAX is to give better solution for broadband by using wireless
infrastructure.
HSDPA
High-Speed Downlink Packet Access (HSDPA) is the 3.5 generation before 4G, which is based on UMTS third
generation network in Release 5. UMTS third generation systems, precise in Release 99 include WCDMA air
interface. High-Speed Up-link Packet Access (HSUPA) and HSDPA belong to the family High-Speed Packet
Access (HSPA). HSPA belong to the WCDMA network, which is upgrade form of 3G network (GSM World,
2009). HSDPA offers maximum output data rates of down-link speeds 3.6, 7.2 and 14.4 Mbps. As compare to
UMTS network, HSDPA provides better quality of service, spectral quality for down-link packet data rate services.
HSPA was planned to offer high data rate at non real time, but after experiment it will show the results for low data
rate application such as VOIP (Holma and Toskala, 2004). In future, Release six and seven would get better look up
for VOIP and related services result of HSDPA.
Comparison: HSDPA vs. WiMAX
HSDPA is an upgrade to the 3G UMTS network, which is primarily designed for voice and WiMAX, which is a
new technology from scratch is designed for data. Competition between the two technologies can’t be avoided at
any cost because of the fact that their primary objective tends to cross into each other; HSDPA is converging
towards data and WiMAX is moving towards voice. It’s the industry is affirmative that the performance of both the
Electronic copy available at: http://ssrnabstract=1829995
technologies won’t be much of importance while deciding which to deploy, but would be their properties which best
fit the operators requirements.
Network architecture
The 3GPP (3GPP, release 6; 3GGP TS25.308, version 5.5.0; 3GGP TS25.855, version 5.5.0) has defined the whole
architecture for the HSPA network, from the edge to the core, from the lowest layer to the highest layer. The IEEE
802-16 specifications only define WiMAX as a technology which supports only the physical and the MAC layer
(Amimo et al, 2007; Smura T, n.d.; WiMAX Forum, 2007).
OPEX and CAPEX
HSPA is just an upgrade to the previously UMTS networks, usually just a software upgrade and/or much as
changing of transceiver at the edge (RNC, Node B). Therefore, unless a new HSPA network is being installed, the
CAPEX (capital expenditure) is very low as compared to WiMAX (Furuskar A et al, 2005). WiMAX on the other
hand is a totally new technology hence operators have to build the network from scratch for which the CAPEX is
quite high for the came coverage as of an HSPA network. The OPEX (operational expenditure) on the other hand
can be treated as nearly the same for both the technologies (Amimo et al, 2007).
Performance analysis
WiMAX uses a higher bit rate modulation coding (64 QAM) then HSPA (16 QAM). 64 QAM is supported by
HSPA release7 which cannot be used simultaneously with MIMO. Release8 of HSPA supports 64 QAM
competitive with WiMAX. HSPA on the contrary has less overhead hence the peak data rate is more than WiMAX
(Anon, 2009). WiMAX beats HSPA release6 as it has better spectrum efficiency. Release7 of HSPA has
comparable spectrum efficiency as compared to WiMAX performance.
Preliminary features of HSPA release8 show better efficiency, then WiMAX (Anon, 2009). Results are similar as
presented by 3G America (3G Americas, 2006).
WiMAX deployed in higher frequencies would have additional losses in link budget as high frequencies tend to
have low range. HSPA operates in lower frequencies leading WiMAX. Still WiMAX has the flexibility to operate in
multiple frequency bands adapting according to the region’s regulations.
Technical Comparison
HSPA and WiMAX both have been designed for high-speed packet switched services. Both technologies are similar
in the case that they support dynamic link adaptation, hybrid ARQ, dynamic scheduling, multi level QoS and
support for smart antennas. Their main difference arises in their operating frequency bands, duplex schemes, and
signal format and handover mechanism (Anon, 2009).
Simulation Environment
The simulations are designed and implemented using MATLAB. Performance is evaluated by transmitting
randomly generated data stream over an AWGN channel with Rayleigh fading. The stream is then received,
demodulated and compared for errors with the theoretical model. MATLAB v7.4.0 (Release: 2007a) was used on
HP work station which was running Microsoft Windows XP professional. Simulations were done in the computer
laboratories in the Section of Teknik at Blekinge Tekniska Högskola, Karlskrona Sweden. The rand () function was
used to create a random data stream. It uses the Mersenne twister algorithm to generate random numbers. Additive
white noise channel (AWGN) model is used to characterize the noise. Rayleigh distribution is used to simulate the
multi path fading effect. Monte Carlo simulation method is used to simulate repeatedly random sampling. In this
method the simulations are repeated with new data each time, BER is calculated each time for every simulation.
Simulation Block (Insert Figure 1)
Simulation Results
The simulation results based upon the adaptive modulation technique are presented in this section. The modulation
techniques used are BPSK, QPSK, 16QAM and 64QAM. All the modulation schemes were used to simulate the real
time environment. Un-coded EbNo vs. BER plots are presented with different modulation schemes. Un-coded data
is considered the channel encoding has not been used.
OFDM simulation with adaptive modulation in AWGN
A random data stream was transmitted using adaptive modulation in an AWGN channel with Rayleigh fading using
256 OFDM pilot carriers. (Insert Figure 2) and (Insert Table 1).
Theoretical values
Theoretical values of BER are presented here for the AWGN and the Rayleigh channel for each of the modulation
schemes used.
AWGN. (Insert Figure 3) and (Insert Table 2).
Rayleigh. (Insert Figure 4) and (Insert Table 3).
Probability of error. (Insert Figure 5) and (Insert Table 4).
Theoretical vs. Actual values
Comparisons between the theoretical BER values for both AWGN and Rayleigh model with the actual values are
presented in this section for all four modulation schemes used.
BPSK. (Insert Figure 6).
QPSK. (Insert Figure 7).
16QAM. (Insert Figure 8).
64QAM. (Insert Figure 9).
Conclusion
The main concentration of this research is on the WiMAX physical layer. Performance is evaluated using an
AWGN and a Rayleigh channel which nearly resembles the real world scenarios. It has been observed that lower bit
rate modulation schemes are better in terms of power efficiency and bandwidth consumption as compared with
other modulation schemes such as QPSK, 16QAM and 64QAM. Higher modulation schemes such as 64QAM
provide high data rates, but are susceptible to higher Bit error rates (BER) on low SNR.
WiMAX adaptable modulation provides best possible error free communications in a wide range of channel
conditions, hence WiMAX provides a better throughput with its fast scheduling as compared to HSDPA. It also
provided better protection against multi path and self interference with scalable channel bandwidth and OFDMA.
The only advantage HSDPA had over WiMAX was it provided better mobility, but with the recent amendments to
the 802.16 standard, WiMAX not even supports mobility, but also supports multi hop relays.