SATNAC 2008 Conference Papers
Access Networks
Title: Efficient Adaptive
Radio Resource Management Algorithms for Next Generation Wireless Systems
Authors: Adeyemi Ajibesin
(
Abstract: The
need for optimised utilisation of scarcely available radio resources is
prevalent. An efficient use of radio resources could lead to higher spectral
efficient transmission on wireless channels. A promising scheme for wireless
multimedia transmission at a lower cost is adaptive modulation and coding
(AMC). In this paper, a new scheme for AMC is devised. A prioritized adaptive
CDMA modulation and a graded resource technique is proposed for the
maximisation of radio resources and for the realisation of next wireless
generation. Rate compatible punctured turbo-code (RCPT) method and diversity
technique with power controlled error (PCE) are also employed for better
results. Simulations were carried out and the proposed algorithms demonstrate
an improved throughput and robustness over the existing systems. These
improvements arise from efficient radio resource management algorithms.
Title: Cross Layer Hybrid
ARQ 2 Cooperative Diversity in Next Generation Wireless Networks
Authors: Sannesh
Beharie (Telkom SA), Hongjun Xu
(
Abstract: Coded
cooperation can achieve diversity through channel coding. The traditional Coded
Cooperation framework is not an efficient transmission scheme since in some
cases the base station has already decoded a particular set of information bits
using a user’s initially transmitted parity and not all parity bits are
required. The user however is not informed by the base station of this. This paper proposes an efficient transmission
scheme called Cross Layer Hybrid ARQ 2 Cooperative Diversity (HARQ 2). By
combining HARQ 2 (at the link layer) with Cooperative Diversity (at the
physical layer) feedback from the base station is available for users. Users
can then transmit incremental parity packets and await feedback from the base
station to decide whether further parity is required for a particular set of
information bits. Improvements in Bit Error Rate (BER) and throughput are
observed by the cross layer design over Coded Cooperation. BER theoretical
bound analysis is performed and is validated by simulations in a block fading
channel.
Title: A Digital Modem Card
for a Multi-channel Satellite Communications Payload
Authors: Kobus Botha
(
Abstract: This
paper describes the design of a digital modem card for use within a
multichannel communications payload for a low earth orbit microsatellite. The payload provides multiple channels
enabling high-speed data transmission of messages to and from rural areas that
fall outside normal terrestrial coverage.
Designing a prototype was the goal of the first phase of the project and
the modem card is a subcomponent of the entire payload. The modem card is based on an interface card
from the SumbandilaSat project and consists of various ICs, a signal processor
and interfaces to other boards. The
design of the software modem and the digital design of the card combined with
the simulation and testing to date show that a complete implementation is
feasible
Title: High Rate Non Binary
Generalized Low Density Parity Check Codes
Authors: Farzad
Ghayour (
Abstract: In
this paper, the construction of high rate non-binary code adapted from
generalized low density (GLD), where as component codes Reed-Solomon codes are
used is investigated. Two different decoding algorithms for the communication
over additive white Gaussian noise channel are used and the complexity and
effectiveness of each one is studied. The performance in terms of bit error
rate obtained by computer simulation and compared to same length Reed-Solomon.
Title: An Application of Deterministic
Network Coding in MANETs
Authors: Leenta Grobler
(
Abstract: Recent
advances in methods to increase network capacity has lead to the introduction
of a new concept called Network Coding. Network Coding holds the promise of
increasing capacity in MANETs as well. However, very few practical results and
implementations are available. In this paper we propose the use of
deterministic Network Coding in a MANET. We present and describe the tools used
to implement and investigate this new method.
Title: A Dynamic Radio
Channel Assignment Scheme for Multi-Radio Wireless Mesh Networks
Authors: Tope Kareem
(Meraka Institute), Karel Matthee (Meraka Institute), Anthony
Chan (
Abstract: This paper
investigates the challenges involve in designing a dynamic channel assignment
(DCA) scheme for wireless mesh networks, particularly for multi-radio
systems. It motivates the need for fast
switching and process coordination modules to be incorporated in DCA algorithm
for multi-radio systems. The design strategy is based on a reinterpretation of
an adaptive priority mechanism as an iterative algorithm that recursively
allocate a set of channels to radios in a fair and efficient manner in order to
minimise interference and maximise throughputs. The algorithm, called Adaptive
Priority Multi-Radio Channel Assignment (APMCA) is tested for overall
performance to assess the effectiveness by determining its overall
computational complexity. The combined advantages of fast switching time and
process coordination modules make the APMCA a useful candidate towards
automating the channel assignment method in multi-radio wireless mesh network
planning and design.
Title: A Fixed-Point DSP
Architecture for Software-Defined Radio
Authors: Wouter
Kriegler (
Abstract: Software-defined radios (SDR)
perform signal processing in the digital domain, replacing hardware that
previously performed such processing. The need exists to rapidly create new SDR
applications without designing an entire system from the ground up, and without
specialized knowledge of a target platform. This paper describes the design of
a generic SDR topology that is highly reconfigurable and promotes a high level
of code re-use. The research forms part of a larger project to design a
domain-specific language (DSL) in which to describe SDR functionality in a
platform-independent way. In this paper, the code synthesis from the DSL is
extended to support the Freescale DSP563xx family, and the study provides a
roadmap for the creation of such extensions to other embedded platforms.
Authors: Blessing
Makumbe (
Abstract: This
paper investigates the performance of Space Time Block Codes (STBC) in a
spatially correlated channel as well as imperfect channel estimation errors.
The spatial correlated channel model used is the kronecker model and the
simulation results are limited to a 2*2 system. Channel estimation errors are
also introduced into a system with and without the kronecker model. Results
show that a 2*1 system is greatly affected by channel estimation errors at high
channel estimation error dB. The perfect 2*2 system (Alamouti 2*2scheme with
rayleigh fading only) outperforms the
kronecker 2*2 system and both systems show a similar trend in performance under
channel estimation errors. However, it is shown that the performance of
kronecker 2*2 STBC is not linearly related to perfect 2*2 STBC therefore making
it important to study the effects of channel estimation error on the former.
Title: Turbo Coded
Cooperation using the Forced Symbol Method
Authors: Jules Mouatcho Moualeu (
Abstract: Diversity
is an effective technique in limiting the deleterious effects of fading, hence
improving the data rate as well as the bit error rate performance. Transmit
diversity is impractical in some scenarios where mobile units, due to size,
hardware complexity and other constraints cannot accommodate multiple antennas.
Recently, cooperative diversity has been introduced where single-antenna
mobiles achieve uplink transmit diversity by relaying each other’s
messages. A particularly powerful variation of this principle is coded
cooperation which partitions the codewords of each mobile and transmits
portions of each codeword through independent fading channels. Coded
cooperation framework has been easily extended using turbo codes, since
cooperative coding contains two codes components. This paper presents an
extension to turbo coded cooperation using the force symbol method. Simulation
results show that the proposed method outperforms the conventional turbo coded
cooperation under different inter-user channel SNRs.
Title: Effects of Rain on
Microwave Remote Sensing Systems and Ground-Based Radars Use in Durban
Authors: Chrispin
Mulangu (
Abstract: In
this paper the result shows that for rainfall intensity below about 10 mm/h for
JD, JT, MP and LP distributions and below about 4 mm/h for TS, TT, CT and CS
distributions the specific rain backscattering follows Rayleigh scattering law
where the rain drops are small with respect to the wavelength when the
frequency is 19.5 GHz. At rain rate more
than 10 mm/h for exponential distribution and more than 4 mm/h for lognormal
distribution, the specific backscattering follows Mie scattering law. When
received echo power from rain becomes significant, it contributes to the rise
in the noise floor and the radar can lose the target. Also the result shows
that Mie backscattering efficiency is highest at raindrop diameter equals of
4.7mm.
Title: Vertical Handoff Decision Algorithm Based on
Fuzzy Logic and Genetic Algorithm
Authors: Yaw Nkansah-Gyekye (University of
the
Abstract: The integration of diverse but complementary cellular and wireless technologies in the next generation of wireless communication systems requires the design of intelligent vertical handoff decision algorithms to enable seamless terminal, personal and network mobility, and to provide for continuity and transfer of existing sessions. This paper provides an adaptive multiple attribute vertical handoff decision algorithm that enables wireless access network selection at a mobile terminal using fuzzy logic concepts and a genetic algorithm. A performance study using the integration of wireless wide area networks (WWANs) and wireless local area networks (WLANs) as an example shows that our proposed vertical handoff decision algorithm is able to determine when a handoff is required, and selects the best access network that is optimized to network conditions, quality of service requirements, mobile terminal conditions, user preferences, and service cost.
Title: A Modem Link Strategy
for Optimization of LEO Satellite Throughput
Authors: Francois
Olivier (
Abstract: This paper presents a means for
optimizing the data throughput for low earth orbit (LEO) satellites by
implementing a mission specific error control strategy. Due to limited
connectivity and very limited overflight time exposure offered by LEO
satellites, it is imperative to volumetrically optimize the data throughput.
With power limitations on the space segment and remote groundstations, hardware
utilization efficiency need to be optimized to reduce power consumption. Most
protocols focus on correcting congestion related link errors, but with beam
shaping introduced for satellite communication, error control strategies
optimized for correcting link related bit errors need to be investigated and
implemented. Low density parity check (LDPC) codes have been shown to achieve
error performance near the
Title: Rainfall Rate
Characteristics for the Design of Terrestrial Link in South Africa
Authors: Pius Owolawi (
Abstract: Rain
attenuation can have a serious impact on the availability of radio
communication system especially at centimeter and millimeter wavelength. In
order to predict reliable rain attenuation for a given location, it is
therefore essential to determine characteristics of rainfall rate at the
location of interest which is geographically dependent. In this paper, the
cumulative distributions, seasonal variability, worst month of rainfall rate
for four locations in
Authors: Olutayo
Oyerinde (
Abstract: Availability of channel state information (CSI) at any communication receiver is important for accurate detection and decoding of transmitted signals. Different types of algorithms have been proposed for the estimation of channel impulse response (CIR) of a time varying channel among which are the least mean square (LMS) and the recursive least square (RLS) algorithms. In this paper we propose a variable step size algorithm for adaptation of CIR estimate by channel estimator incorporated into turbo receiver for turbo code. The soft information feedback from the turbo decoder, which is based on low-complexity soft-input/soft-output (SISO) equalization algorithm a time-varying CIR, is used to improve the channel estimate over a number of iterations. The channel estimate is employed by a turbo equalizer to remove the effect of intersymbol interference imposed by the communication channel. The proposed algorithm alongside other algorithms has been used for channel estimation in combination with the equalizer. The simulation results for normalized fade rates of fDTs = 0.01 and fDTs =0.005 show how the proposed channel estimation based-algorithm outperforms LMS-based channel estimation algorithm and its performance is very close to that of RLS-based channel estimation algorithm.
Authors: Laneil
Padayachee (
Abstract: This
paper serves as a simple extension to an already proposed scheme for channel
and delay estimation for an asynchronous cooperative diversity network in a
Rayleigh Block-Flat-Fading channel. Pilot symbol design is also discussed for
M-PSK modulating schemes. It is also shown that the Cramer-Rao lower bound for
channel and delay estimation is achieved for different delay values.
Title: An Efficient Dynamic
Buffer Allocation Scheme for the Future Internet
Authors: Divya
Pillai (
Abstract: The
current Internet uses a single queue per output port to buffer packets destined
for that port. This often causes congestion leading to packet loss and delay.
Real-time applications are delay and loss sensitive. There is therefore a need to develop a buffer
management system that will effectively accommodate both real-time and
non-real-time applications. In this paper, we propose a dynamic threshold
buffer management scheme. This scheme uses
complete sharing with virtual partitioning. Pre-emption is used to
minimise congestion. Out of profile high priority packets are dropped during
pre-emption period. To add fairness to the scheme, low priority packets are
guaranteed a minimum buffer space.
Title: Carrier Frequency Offset Estimation in WCDMA
Systems Using a Modified FFT-Based Algorithm
Authors: Seare
Rezenom (
Abstract: Wideband
Code Division Multiple Access (WCDMA) is one of the wireless access
technologies that delivers high data rates for the third generation
communication systems. It uses different scrambling codes to differentiate
among base stations. The receiving terminal needs to decode the correct
identity of the scrambling code. The Fast Fourier Transform (FFT) technique is
used to estimate the carrier frequency offset in a WCDMA system. This paper
discusses the FFT based estimation technique and proposes a new method that
employs overlapping partition sequences of the FFT window. The proposed method
is compared to the conventional non-overlapped algorithm.
Authors: Oludare
Sokoya (Meraka Institute), Sunil
Maharaj (
Abstract: The
performance of space time trellis coded orthogonal frequency division
multiplexing (STTC-OFDM) systems relies on accurate channel state information
at the receiver for proper decoding. One
method of obtaining channel state information state information is by inserting
known pilot symbols periodically at the transmitted symbols. This paper
investigates the performance of the STTC-OFDM system when non overlapping pilot
structures are employed in channel estimation at the receiver. In this paper,
the Frame Error Rate (FER) and Bit error rate performance of the STTC-OFDM
scheme under various channel delay spread is compared with the case when
channel state information is present at the receiver.
Title: Evaluation of 3GPP
LTE and IEEE 802.16 as Candidate IMT-Advanced Systems
Authors: Ryan van den Bergh (University of the
Witwatersrand), Hu Hanrahan (University of the
Abstract: In 2003 the ITU-R published Recommendation M.1645 outlining the ITU’s vision for the development of 4G systems. In 2007 the ITU initiated the standardisation of 4G, which they named IMT-Advanced systems. Currently the ITU is inviting interested parties to submit proposals for their mobile communication systems to be considered for inclusion in the IMT-Advanced standard. Two such candidate systems are the 3GPP’s LTE standard and the IEEE’s 802.16 WiMAX standard. This paper outlines both systems’ requirements and architectures and evaluates their potential to meet the requirements specified for IMT-Advanced. Based on the analysis conducted, it was determined that both systems meet the preliminary requirements specified. Future work must be conducted to refine the IMT-Advanced specifications and additional candidate systems need to be investigated to determine their potential to be included in the final version of the standard.
Title: Towards Gigabit DSL
(GDSL): System Feasibility Study
Authors: Jacques
van Wyk (
Abstract: With
the introduction of VDSL2 and the implementation of Fibre-to-the-Curb (FTTC),
the theoretical limit of DSL technology is pushed even further than currently
known ADSL technology. Current research is investigating the possibility of
symmetric DSL at 1 Gbps (GDSL). This paper follows on a SATNAC 2007 paper and
addresses a study on the feasibility of a complete complementary multi-carrier
code-division multiple access (CC/MC-CDMA) transceiver system. This fully
functional modem combines the virtues of both orthogonal frequency division
multiplexing (OFDM) and conventional code division multiple access (CDMA) to
support many users simultaneously with higher spectral efficiencies than
conventional CDMA systems and better noise tolerance than existing DSL
solutions. We also determine the capacity of the CC-MC-CDMA system.
Title: Combating the effects
of Hidden Terminals in Multi Channel MAC Protocols
Authors: Mthulisi
Velempini (
Abstract: Multiple channels present IEEE
802.11 MAC protocol designers with a number of options in their attempt to calm
the effects of Hidden Terminal Problems (HTPs). The research on multi-channels
shows that the effects of HTPs can be reduced and limited to Request To
Send/Clear To Send (RTS/CTS) control packets. Unfortunately our analysis shows that data packets can be affected by
HTPs. An effective HTP control channel solution may effectively protect data
packets in data channels. Our previous work revealed that HTPs can be
completely eliminated through the implementation of Long Inter- Frame Space
(LIFS) and an intelligent MAC in single channel systems. An intelligent MAC
divides terminals into two segments, the Transmitter Carrier Sensing Zone (CSZ)
and the Receiver CSZ for the implementation of Extended Inter-Frame Space
(EIFS) and LIFS respectively. The extension of our LIFS and CSZ concepts to
Multi-channel environments reveals interesting developments that need to be
tackled. The HTP may not be completely eliminated as new challenges arise in
multichannel environments. Multiple channels have a delayed effect on HTP
manifestation. They do not solve the HTP but they reduce its effects. Our
analytical results suggest the existence of a theorem mapping the occurrence of
HTPs onto the number of channels implemented.