We study the data performance of WCDMA systems using the downlink shared channel (DSCH) by investigating the impact of loading, rate adaptation and power control for the typical urban (TU) channel. We conclude that, using DSCH, high speed data transmissions can be achieved if the offered traffic load is well controlled. We discuss a heuristic rate adaptation algorithm that adapts the transmission rate based upon the perceived user performance in previous frames. We show that the performance of the rate adaptation is significantly better than that for the fixed-rate allocation policy.

Traditionally, packet scheduling has been considered to be the primary technique for providing quality of service in communication networks. In a previous paper (see IEEE Globecom '00 Proc., vol.3, p.1515-21, Nov. 2000) we explored different packet scheduling techniques for providing differentiated services (premium vs. basic service offerings) in the 3G EGPRS (enhanced general packet radio services) system. A premium service is defined here as one with a higher priority, and therefore resulting in a better user experience, than a basic service. This paper continues the investigation. In particular, we assess algorithms that allocate multiple time slots for premium users. The results show that multi-time slot assignment for premium users is very effective in supporting differentiated service offerings. It provides a better user experience to premium users with little performance degradation to the basic users.

We investigate the performance of voice and best-effort data traffic over Enhanced General Packet Radio Services (EGPRS) using tight reuse configurations (e.g. 1/3 or 1/1), with the aim of identifying suitable bearer designs and optimal system configurations for these services. We find that voice and data have somewhat conflicting preferences: voice capacity is optimized using random frequency hopping and quality-driven power control: data throughput is optimized using no frequency hopping and no power control. These somewhat contradictory requirements impose a challenge in the system design. We investigate two simple traffic integration strategies: (1) segregating the resource for the two services and using the optimal configuration in each segment; and (2) integrating the traffic by allowing voice and data to share the same resource, and use a compromised configuration for the entire system. We find that if the majority of traffic is voice, traffic integration has an advantage since data can use any residual voice capacity. On the other hand, if the majority of traffic is data, segregation provides higher spectrum efficiency. Furthermore, the integrated traffic option becomes increasingly sub-optimal with increasing data traffic load. We conclude that the system design should depend upon the expected mix of traffic (including traffic types in addition to voice and best-effort data) and the desired engineering complexity, and that further work is needed to understand the possible design options. One possible design option is to soft segregate the resource, e.g., to allow data to use the voice segment on an overflow basis. Similar strategies may be good avenues for future work.

Using the MPEG-4 advanced audio coder (AAC) music as an example of streaming applications, we investigate the improvement of error performance for the streaming service by link adaptation and power control techniques in an enhanced general packet radio services (EGPRS) cellular network. A low packet error rate and variability are essential in providing a short error-burst length so that error concealment techniques can be effectively applied to music packets. We study the effects of a combined link adaptation and power control scheme (referred to as the error-based scheme) for achieving a target error rate and reducing error variability. By simulation, we compare the error performance of the error-based scheme at both the EGPRS block and AAC frame level with another adaptation algorithm (referred to as the throughput-based scheme) with a goal of maximizing overall network throughput. It is found that when offered with a similar traffic load, the former scheme can provide noticeable improvement of music quality over the throughput-based scheme. To achieve a similar AAC frame error rate, our results also show that the error-based scheme can increase the link throughput over the throughput-based scheme by 66.7% in one of our examples. These results reveal that by aiming at required error targets and thus reducing error variability, the error-based scheme for link adaptation and power control are helpful in improving quality and capacity for streaming applications.

We propose a framework for network-assisted radio resource management in wireless data networks. This type of radio resource management techniques offer implementation and capacity benefits compared to conventional, interference-measurement based, dynamic channel assignment (DCA) algorithms. The basic idea is to use interbase signaling to shift most of the burden of the resource allocation from the air interface to the backbone infrastructure. By exchanging channel assignment as well as other relevant information in real time through the backbone network, each base can calculate the impact of a resource assignment on the system. As a result, rapid interference measurements, which are typically needed to implement DCA schemes, are replaced by a limited amount of path loss measurements and the computation of interference conditions by the base stations. This significantly reduces the measurement and over-the-air signaling requirements, and can also provide an opportunity for a better optimization of the system performance. We focus on two specific algorithms: network-assisted least-interference-based dynamic packet assignment (NA-LI-DPA) and network-assisted dynamic packet assignment with throughput optimization (NA-DPA). NA-LI-DPA closely resembles a least-interference-based dynamic channel assignment algorithm, and NA-DPA attempts to further improve the overall system throughput. The algorithms, as defined, are appropriate for a best-effort data service, where the primary goal is to provide a higher throughput. However, it will be clear from the discussion that it is also feasible to alter the algorithms to optimize performance metrics other than throughput, e.g., to ensure a certain quality of service. We show through simulation that, for a system like enhanced general packet radio service (EGPRS) system, NA-DPA can provide a throughput that is 50% higher than random packet assignment, and 25% higher than that obtained by conventional DCA algorithms.

This paper discusses the feasibility of offering multiple service classes, e.g., premium and basic, in the 3G EGPRS (Enhanced General Packet Radio Services) system using different scheduling mechanisms. We investigate weighted round-robin type scheduling for differentiating the service classes together with two types of packet schedulers: radio-aware packet schedulers at the radio access network, and conventional packet schedulers at the edge of the core network. The results show that for the EGPRS-like system simulated: (i) incorporating radio link conditions and radio resource management into the scheduling can improve the overall delay performance by more than 20%; (ii) a weighted round-robin scheduling to differentiate service classes may not be suitable for an interference limited environment. Our ongoing work will consider using multiple time-slot assignments for providing differentiated services.

We investigate the ability of multiple descriptions (MD) and layered coding to improve the quality of video transmitted over EGPRS networks. One-layer video sent over a single channel on such a network has a fairly sharp quality transition, depending on a user's location. Either the video can be transmitted reliably (if the video rate is less than or equal to what the channel can sustain), or it is subjected to many lost packets. In this system, MD and layered video may offer two ways to improve the video quality beyond that of the one-layer video. First, each sub-stream can be sent on a separate channel, essentially doubling the assigned bandwidth and increasing the video quality. Second, MD and layered video are more error resilient than one-layer video, potentially improving the video quality seen by users in poor locations. We find that for the system scenarios considered, one and two-layer coding outperform MD coding, depending upon the number of wireless channels used for the video transport.

We investigate the possibility of supporting voice over EGPRS as a potential evolutionary path for 2/sup nd/ generation wireless TDMA systems. We discuss different voice bearer designs for EGPRS radio access networks. We demonstrate how the operating mode can be chosen at each layer in the protocol stack to form appropriate voice bearers, and quantify the performance of these bearers. Different system control options are examined, including frequency reuse factor, MAC layer operating mode, frequency hopping, power control, and dynamic channel assignment. We find that a baseline EGPRS system using random channel assignment and no power control can support up to 27 Erlang/Site/MHz, which is significantly higher than the capacity of current 2/sup nd/ generation TDMA systems. In addition, the packet-switched nature of EGPRS makes it a very flexible system. We conclude that EGPRS offers an excellent evolutionary path for 2/sup nd/ generation TDMA systems.

We propose a network-assisted radio resource allocation algorithm for wireless data networks with synchronized base stations, which support variable rate transmission. The algorithm, Soft-Bar, may be used in both mobile and fixed wireless systems to assign the channel, transmission mode and transmit power for each user, and may be implemented in a distributed manner. The basic idea of the algorithm is to use measurements at the base and the terminal, and limited, real-time inter-base signaling, to control the interference generated by the few dominant interferers for each user. We show that in an EDGE-like system using 1/3 reuse, compared to conventional random packet assignment, Soft-Bar can (1) increase the system throughput by more than 50% for a given delay constraint; or (2) increase the number of users by more than 30% for a given user outage requirement, while at the same time improving the user experience. In addition, it can facilitate QoS provisioning in a straightforward manner.

We examine the feasibility of supporting integrated services, such as packet voice, Web browsing, and best-effort data, using Enhanced General Packet Radio Services (EGPRS). Among many factors that need to be considered, we focus on enhancing the radio link control/medium access control (RLC/MAC) layer design to support such services. We first describe the relevant capabilities offered by the current standard, and then outline additional capabilities that are needed at RLC/MAC layer to support real-time services. In summary, these needed capabilities are: (1) fast uplink access during an ongoing session; (2) fast resource assignment for both uplink and downlink; and (3) the ability to differentiate services at the base station sub-system. To realize these capabilities, we propose enhancements to the RLC/MAC layer, including: (1) a new set of packet control channels; (2) uplink access protocols that utilize these control channels; and (3) a new access request identifier. These changes would enable EGPRS to offer a wide range of services through a single packet based network.

The use of microcells is an attractive option for providing high data rate access for fixed and low mobility users. We propose and analyze a wireless backhaul network for connecting microcells to the wireline network. In the proposed network, several microcellular radio ports are connected to a so called hub through radio links. These hubs are then connected to the wireline network using cable or fiber. For ease of deployment, we propose that omnidirectional antennas be used at the radio ports and sectored antennas be used at the hubs. Our results show that for 95% of the links, a link reliability of 99% may be achieved with an effective frequency reuse of 3 by using site-selection, flexible channel assignment, power control and two-branch minimum mean square error combining. For the remaining 5% of the more vulnerable links, a direct wireline connection may be provided. We also find that power control plays a critical role in reducing the variation of the link performance over time. In addition, the best performance is achieved by jointly optimizing the receiver, i.e., the diversity combining weights, and the transmit power settings. We show that this joint optimization may be implemented in a distributed manner, making it attractive for use in real systems.

Link adaptation and incremental redundancy are two link level techniques proposed to enhance data rate and increase throughput in wireless data networks. Link adaptation pro-actively adjusts the modulation and coding scheme based upon estimated channel conditions. Incremental redundancy, on the other hand, adjusts the code rate to actual channel conditions by incrementally transmitting redundancy information until decoding is successful. In this study, we investigate the system performance of these two techniques. Our results show that incremental redundancy achieves significantly higher throughput compared to link adaptation, especially under high traffic loading conditions. This gain is achieved at the expense of higher terminal and base station complexities, as well as a higher packet delay. On the other hand, in contrast to link adaptation, incremental redundancy does not require any channel quality measurements, and can operate based solely upon ACKs and NACKs.

We propose a novel intercell interference management technique, called quasi-static resource allocation with interference avoidance (QRA-IA), for fixed broadband wireless systems with narrow sectors or equipped with fixed or adaptive array antennas. The basic idea of QRA-IA is for every base to periodically turn off each of its beams (sectors) for a certain amount of time. This periodic turn off introduces a predictable nonuniformity in a terminal's performance and therefore permits each terminal to identify a preferred time period for transmission. QRA-IA requires that each terminal sense the interference over time, select the preferred transmission periods, and report these to the base. The resource allocation algorithm at the base can then use this information for scheduling transmissions to the terminals. The base can also use this information for obtaining an appropriate beam-off sequence. A graph theory model is used to show that an acceptable beam-off sequence exists for each base. A simple, distributed, and measurement-based beam-switching algorithm is designed for the system to find these sequences autonomously. We demonstrate via simulations that a system with QRA-IA provides a marked improvement in the packet error rate performance of terminals over the same system without QRA-IA. This improvement translates directly to improved coverage and throughput and also reduces the burden on higher layer protocols to ensure fairness and quality of service.

Adaptive modulation techniques have the potential to substantially increase the spectrum efficiency and to provide different levels of service to users, both of which are considered important for third-generation cellular systems. In this work, we propose a general framework to quantify the potential gains of such techniques. Specifically, we study the throughput performance gain that may be achieved by combining adaptive modulation and power control. Our results show that: (1) using adaptive modulation even without any power control provides a significant throughput advantage over using signal-to-interference-plus-noise ratio (SINR) balancing power control and (2) combining adaptive modulation and a suitable power control scheme leads to a significantly higher throughput as compared to no power control or using SINR-balancing power control. The first observation is especially important from an implementation point of view. Adjusting the modulation level without changing the transmission power requires far fewer measurements and feedback as compared to the SINR-balancing power control or the optimal power control. Hence, it is significantly easier to implement. Although presented in the context of adaptive modulation, the results also apply to other variable rate transmission techniques, e.g., rate adaptive coding schemes, coded modulation schemes, etc. This work provides valuable insight into the performance of variable rate transmission techniques in multi-user environments.

In this paper, we propose an inter-cell interference management technique, called dynamic resource allocation with interference avoidance (DRA-IA), for fixed broadband wireless systems with narrow sectors or equipped with fixed or adaptive array antennas. The basic idea of DRA-IA is for every base to periodically "turn-off" each of its beams (sectors) for a certain amount of time. This periodic turn-off introduces a predictable non-uniformity in a terminal's performance, and therefore permits each terminal to identify a preferred time period for transmission. DRA-IA requires and that each user sense the interference over time, select the preferred transmission periods, and report these to the base. The resource allocation algorithm at the base can then use this information for obtaining the appropriate "beam-turn-off" sequence and for scheduling transmissions. We demonstrate that DRA-IA provides a marked improvement in the packet error rate performance of "disadvantaged" terminals. This improvement translates directly to improved coverage and throughput, and also reduces the burden on higher layer protocols to ensure fairness and quality of service.

A wireless office service (WOS) system is a virtually self-contained cellular system for providing wireless service in an office or campus environment. It co-exists with, and uses the same technology and spectrum as the surrounding public wireless system. For such systems to be viable, it is necessary to automate their RF (radio frequency) engineering process, and even to make them "self-engineering". We devise procedures and algorithms to achieve this self-engineering at system-startup, and then validate them through simulations. Although designed for in-building or campus environments, with suitable modifications these procedures and algorithms may be applicable to more general scenarios.

A wireless office service (WOS) system is a virtually self-contained cellular system for providing wireless service in an office or campus environment. It co-exists with, and uses the same technology and spectrum as the surrounding public wireless system. These systems are assuming increasing importance with increasing demand for consistent services from a single phone while in all environments: home, office, and at large. For these systems to be viable, it is necessary to automate their RF (radio frequency) engineering process, and even to make them "self-engineering" or "self-adapting". We discuss procedures to achieve this self-engineering during system operation. Although designed for in-building or campus environments, with suitable modifications, these procedures may be applicable to more general scenarios.

Cellular digital packet data (CDPD) systems borrow idle radio channels from Advanced Mobile Phone Standard (AMPS) cellular networks to send short bursts of packet data traffic. Unless AMPS channels are dedicated to CDPD, utilization of unused AMPS channels results in increased interference for voice. We quantify this increase in interference and show that in many systems the interference "slack" from the radio engineering in AMPS can be exploited to deploy CDPD on channels shared with voice. In particular, we find that this is true for 3-sector cells with 7-cell reuse, a deployment scheme used in many cellular systems.

The authors investigate methods for the parallel acquisition of a PN sequence in a baseband direct sequence spread spectrum system. Four different schemes are considered: the optimal estimation scheme, the maximum-likelihood estimation scheme, a hypothesis-testing scheme that searches over all shifts, and a locally optimum detection scheme. Approximate expressions for the probability of error are derived for the first and last of these schemes and compared with the actual error probabilities obtained via Monte Carlo simulation. Monte Carlo simulation is also used to obtain the error probabilities of the other two schemes and the results for all the schemes are compared. Since the obvious methods of implementing a parallel acquisition scheme require large amounts of hardware or excessive computation, they outline a technique that can be used to reduce the amount of computation.>

The use of a sequential probability ratio test (SPRT) for the acquisition of pseudonoise (PN) sequences in chip synchronous direct-sequence spread-spectrum (DS/SS) systems is considered. The out-of-phase sequence is modeled as a random sequence and the probabilities of error and expected sample sizes for the corresponding test are derived. A different (and very commonly used) test is obtained if the out-of-phase sequence is modeled as a zero sequence. The probabilities of error and the expected sample sizes of both SPRT's are compared, and it is shown that the latter test has a significantly larger probability of type I error. Numerical evaluation of the performance of both tests applied to a PN sequence of period 210- 1 gives results in agreement with the analytical results. We conclude that a random sequence is an excellent model for a PN sequence, and that significant degradation in performance can be expected if the test design is based on the zero sequence model rather than on the random sequence model.

The optimum detection of M orthogonal equiprobable equal-energy signals in additive white Gaussian noise is considered, and two upper bounds for the probability of error are derived. The behavior of these bounds is discussed and they are compared with previously known bounds for various values of signal-to-noise ratio and M. Some numerical results are presented.>