Code division multiple access

We developed a cross layer design which combines retransmission diversity and
multi-user diversity for wireless communication. To this end, a joint design of
adaptive modulation and coding with retransmission-based automatic repeat request
protocol is outlined. This design is applied to devise multi-user scheduling schemes,
which can optimally capture the available multi-user and retransmission diversities. In
addition, the proposed on-line scheduling algorithms can operate even when the
underl ying fading channel distribution is unknown, while asymptotically converging
to the offline benchmark with guarantees on prescribed fairness and rate requirements.
Numerical results are provided to verify the merits of our novel schemes for
multi-user transmissions over Nakagami block fading channels.

One of the biggest factors in the quest to better wireless communication is cellular
call handoff, which in tum, is a function of geographic location. In this thesis, our
fundamental goal was to demonstrate the value addition brought forth by spatial data
visualization techniques for the analysis of geo-referenced data from two different
location tracking technologies: GPS and cellular systems. Through our efforts, we
unearthed some valuable and surprising insights from the data being analyzed that led to
interesting observations about the data itself as opposed to the entity, or entities, that the
data is supposed to describe. In doing so, we underscored the value addition brought forth
by spatial data visualization techniques even in the incipient stages of analysis of georeferenced
data from cellular networks. We also demonstrated the value of visualization
techniques as a verification tool to verify the results of analysis done through other
methods, such as statistical analysis.

Research presented in this thesis develops a mainly theoretical basis and computer
models for enhancing the throughput of multi-user wireless communication networks.
The cross-layer combination of an adaptive modulation and coding (AMC) scheme at the
physical layer and the use of automatic repeat request (ARQ) retransmi ssions at the data
link layer is integrated into a scheduling framework for multi-user networks. Scheduling
algorithms incorporating retransmission diversity are derived for three cases of typical
network traffic: best-effort, non-realtime, and realtime. For each case, numeric computer
si mulations of wireless communications over Nakagami-m block fading channels are
developed to examine the effectiveness of the formulated schemes.

The performance of a multicarrier DS CDMA system is evaluated over a Nakagami multipath fading channel. After the spreading process, the data sequence is applied to multiple carrier rather than a single carrier. Each carrier is provided a corralator in the receiver, and the maximal-ratio combiner is used for the corralator outputs. A bandlimited spreading waveforms are used for self-interference prevention. Robustness to multipath fading and narrow band interference suppression are achieved by this type of configuration. A comparison is made with a single carrier system in the presence of interference.

This thesis presents the simulation based performance evaluation on the transmission of multimedia services (H.264/AVC video streaming) to a mobile user over a packet-switched wireless network based on the WCDMA standard. The H.264/AVC refers to the codec, which is used as the main tool for video compression. It enables the transport of high bandwidth video data over Third Generation (3G) wireless systems by offering a high video compression rate, adaptability to the channel, and error resilience. It is transported using the RTP/UDP/IP protocol stack over the 3G wireless system. The WCDMA technology is simulated with special emphasis on the upper layers of the wireless channel. The performance of the WCDMA system is studied when transporting RTP/UDP/IP packets of H.264/AVC compressed video data under diverse configuration scenarios, namely, ARQ schemes and variable length of the transmitted frame at the link layer. These components of a packet-switched streaming service are integrated into a software simulation model, which is used to evaluate the end-to-end H.264/AVC video quality in a WCDMA wireless network.

The objective of this work is to apply and investigate the performance of a neural network-based receiver for interference cancellation in multiuser direct sequence code division multiple access (DSCDMA) wireless networks. This research investigates a Receiver model which uses Neural Network receiver in combination with a conventional receiver system to provide an efficient mechanism for the Interference Suppression in DS/CDMA systems. The Conventional receiver is used for the time during which the neural network receiver is being trained. Once the NN receiver is trained the conventional receiver system is deactivated. It is demonstrated that this receiver when used along with an efficient Neural network model can outperform MMSE receiver or DFFLE receiver with significant advantages, such as improved bit-error ratio (BER) performance, adaptive operation, single-user detection in DS/CDMA environment and a near far resistant system.

Ad-hoc wireless networks are the networks without an infrastructure. Infrastructure-less mobile networks have no fixed routers or base stations. All nodes in these networks are capable of movement and can be connected dynamically at any time. The issue of routing packets effectively between any nodes in an ad-hoc network is a challenging task. A path that was considered optimal at a given time point may not be working after a few moments. Moreover the bandwidth available between a link may not remain the same since every node in this kind of network is behaving as a router and may experience drastical increase in throughput and traffic load. For the purpose of quality of communication, bandwidth reservation within ad-hoc wireless network nodes may prove promising as a solution to this problem. This thesis presents an approach to reserve bandwidth available utilizing CDMA of bandwidth to the Ad-hoc Distance Vector Protocol for the ad-hoc wireless networks. Various quality of service issues are discussed and are tested for optimal performance for AODV routing protocol. A QoS performance comparison based on mobility, congestion and throughput is made between AODV and CDMA based AODV mobile routing protocols.

This thesis is concerned with the performance analysis of a DS/CDMA packet radio system under Rician fading channel conditions. Analytic expressions are derived for the probability density functions and cumulative distribution functions of the total signal-to-interference ratio when considering mixed-type of interference sources. The users are divided into two groups: those that apply closed-loop power control and those that apply open-loop power control. Four different scenarios of power control were studied. The outage probability is evaluated for the four different cases of power control. A packet transmission protocol with forward error correction capabilities is considered, and the probability density functions of the signal-to-interference ratio are used to calculate the average block error probability as well as the outage probability of the system.

This thesis is an effort to present the performance analysis of the RLP in cdma2000, which uses the NAK based ARQ scheme for Random Error Channels. The performance analyses is done in terms of throughput and mean extra delay, which are calculated analytically and are compared with the results generated from the simulations. As the demand for higher data rates increases over the wireless channels, this thesis studies the effect of the random errors over the different types of RLP frame formats and also the performance of the NAK based ARQ mechanism used in these conditions. The simulation provides with the overall characteristics of the throughput and the mean extra delay in terms of realistic environment parameters like Eb/No and probability of packet error (Pe), based on the channel conditions.

The performance aspects of conventional cellular (FDMA/TDMA) and CDMA systems with micro- and macroscopic diversity reception are investigated in a severe mobile communication environment which is characterized by path loss, correlated lognormal shadowing, multipath fading, background noise and interference. Under a co-channel interference-limited assumption, an exact analytical expression for the co-channel interference (CCI) probability is presented for a macroscopic diversity system with an arbitrary number of correlated macroscopic branches. For noise-limited systems, the average bit-error-rate (BER) and outage probability performances of a narrowband mobile communication system with micro- and macrodiversity reception are evaluated. In the relevant analysis, both Nakagami and Rician fading channels are considered. When both co-channel interference and noise coexists, the results for a Nakagami fading channel show that diversity reception can be used to reduce the effects of interference while combating fading and shadowing. Micro- and macroscopic diversities are also applied to a multicell DS-CDMA system. In a conventional cellular system with macroscopic diversity, the mobile user is usually connected to the closest base station. However, a base-station selection scheme based on a least attenuation criterion is shown to provide a significant performance improvement over the conventional system. In this case, the system performance is examined in terms of BER and outage probability, while accounting for the effects of path loss, correlated shadowing, multipath fading, multiple access interference, and imperfect power control.