A Linux-based EGPRS (enhanced General Packet Radio Service) real-time test bed software is presented. It uses a Markov model to emulate the time-varying EDGE radio channel characteristics in real time, where the model parameters are obtained from intensive large-scale system simulations. The test bed is designed as a platform to test/evaluate wireless QoS scheduling algorithms for the EGPRS radio access network as well as for the EGPRS core network. It is implemented in the TCP/IP stack of the Linux operating system. The EDGE radio channel emulation, radio-aware packet scheduling algorithms, and radio resource management methods are implemented in a virtual network device driver as an intermediate layer between the IP layer and the physical Ethernet card driver, while packet scheduling algorithms for the EGPRS core network can be accommodated in the IP layer as regular QoS routing modules. Using a Web-based test bed controller, one can set up radio system configuration and PDP context parameters for the test bed, and monitor traffic statistics such as instantaneous transmission rate, instantaneous and accumulated queue length, accumulated queue length norm, and accumulated number of transmitted and retransmitted bytes. Some experimental results are given to demonstrate the use of the test bed.

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.

Abstract Performance enhancing proxies have drawn considerable interests from the network community as an effective approach to improve user experience in cellular networks. Previous research on this subject has been focusing on the design of proxy servers as well as the functions that these servers provide. In this paper, we study the placement of proxy servers, especially the approach of incorporating proxies into cellular networks, which allows better, faster, and more secure proxy services. We discuss various factors that must be considered when placing proxies inside cellular networks, including the information requirements of the proxies, the network requirements for supporting the proxy functions, and mobility management. Using GPRS as an example, we lay out a procedure for adding proxies into data transmission paths in cellular networks. Copyright © 2001 John Wiley & Sons, Ltd.

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.

This paper evaluates the use of packet scheduling to provide multiple service classes for bursty data traffic. In particular, we study the performance of the weighted fair queueing algorithm by simulating various scenarios in a packet cellular wireless network similar to an EDGE (Enhanced data rate for GSM evolution) system. The results show that, due to the burstiness of data traffic, traditional work-conserving packet scheduling algorithms such as weighted fair queueing cannot achieve the desired performance unless the system is heavily loaded. Similar results hold even when using priority queueing, which is an extreme form of weighted fair queueing. We also find that best effort traffic should be managed carefully to avoid inefficient usage of the network, especially in a low capacity cellular environment.

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.

Performance enhancing proxies have drawn considerable interests from the network community as an effective approach to improve user experience in cellular networks. Previous research on this subject has been focusing on the design of proxy servers as well as the functions that these servers provide. We study the placement of proxy servers, especially the approach of incorporating proxies into cellular networks, which allows better, faster, and more secure proxy services. We discuss various factors that must be considered when placing proxies inside cellular networks, including the information requirements of the proxies, the network requirements for supporting the proxy functions, and mobility management. Using GPRS as an example, we lay out a procedure for adding proxies into data transmission path in cellular networks.

This paper reports on studies of the effects of the TCP/IP protocol header on the system performance of a spectrally efficient cellular system. Integrated cellular system and TCP-protocol simulations are used to examine the degradation in the effective data throughput and packet delay due to the header overhead. Performance improvements achievable by header compression are investigated. Simulations have been designed for an EDGE-like cellular system. System-wide performance is examined using cumulative distributions for data throughput, delay and packet success. For example, the data throughput of a micro-cellular system with Web traffic is improved about 10% when header compression from 40 to 2 bytes is implemented. More aggressive compression yielded minimal further improvements.

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 mobile IP (MIP) protocol for IP version 4 provides continuous Internet connectivity to mobile hosts. However, currently it has some drawbacks in the areas of survivability, performance, interoperability with protocols for providing QoS. We have proposed an alternative protocol, mobile IP with location registers (MIP-LR), which overcomes some of these drawbacks and is closer to the "service node" database approach used in the public switched telephone network (PSTN): before launching a packet to the mobile host, the sender first queries a database, called the home location register (HLR), to obtain the recipient's current location. MIP-LR is designed for operation in enterprise environments or within logical administrative domains. We focus on showing how MIP-LR enhances the survivability of MIP by eliminating some of the functions which MIP introduces for mobility support, allowing the HLR to be placed outside the mobile's home network in case the latter is particularly vulnerable, and replicating and distributing HLRs. We present two schemes for managing the multiple HLRs and enabling mobile and correspondent hosts to dynamically discover the addresses of the HLRs serving a given mobile host. The first scheme introduces a set of translation server (TS) databases while the second uses a form of quorum consensus based on the triangle lattice (TL); for the latter we present an enhanced protocol called the optimistic TL(OTL). For both schemes we present algorithms for mobile host registration and packet delivery, protocols for recovery from HLR failures, and complexity analysis of the overhead involved.

As the growth rate of the Internet subscription increases, the demand for providing wireless access for Internet applications becomes apparent. While packet data networks like CDPD, RAM, and Metricom provide Internet services, their channel capacity is generally insufficient for Internet applications such as Web browsing. Asymmetric high-speed wireless access techniques that support wide-area high-speed Internet applications have been studied and investigated extensively in the industry. However, the network architecture to support interworking of the high-speed wireless access network with the Internet has not been widely discussed. This paper addresses architecture alternatives for interworking of high-speed wireless access network, with Internet backbone for providing a seamless wide-area wireless Internet access service.

With the increased subscription rate in Internet services and wireless communications services, a significant amount of traffic for the future wireless communications will be from Internet applications. Therefore, it is important to design a bandwidth-efficient channel allocation scheme to support Internet traffic, which are packet-switched in nature. Dynamic channel assignment (DCA) schemes are believed to achieve higher system capacity and spectrum efficiency in a frequency-reuse wireless system without frequency planning. This makes DCA a suitable candidate to provide high-speed wireless packet data services. This paper investigates the performance of two distributed measurement-based DCA schemes under Pareto-distributed packet data traffic, a well-known traffic model with heavy-tailed distribution and infinite variance. Performance comparisons of DCA schemes under different wireless packet data traffic conditions are also presented. The sensitivity of the channel setup delay on the SIR performance at access are discussed. These results can provide guidelines for the future design of DCA and medium access control (MAC) protocols for wireless Internet services.

We present an analysis of the relationship between the two link-level QoS (quality of service) parameters (delay and error rate) and the motion speed of a user in a wireless packet network environment. The analysis is based on: (1) a wireless channel simulation using a time-correlated Rayleigh fading model and (2) a physical layer model which complies with the wireless LAN draft standard, IEEE 802.11. The analysis on delay and error rate QoS parameters is targeted to two major types of network applications: (1) real-time applications which are sensitive to delay but can tolerate a small amount of data loss and (2) conventional data transfer applications which are sensitive to data loss but normally do not require specific delay bounds.

Recently, the CDMA Development Group (CDG) and TIA-TR45.5 have been considering proposals using multiple codes to provide high-speed data services in IS-95 CDMA systems. Though some aspects of the high-speed CDMA performance have been studied previously, the impact of bursty data traffic dynamics has not been fully investigated. This paper evaluates the high-speed CDMA system performance with mixed voice and bursty data traffic in the presence of shadow fading. The simulation results suggest that a burst/call admission policy based on both data subscriber location and data/voice traffic loads is required for good performance. In addition, the conventional analytical model based on mean values may be too optimistic and the analysis assuming that the data subscribers are always transmitting may be too pessimistic to evaluate the system performance.

The users of third generation personal communications services (PCS) will be applications with diverse quality of service requirements. This work addresses the fixed network delay of call setup in a personal communications network (PCN) architecture with wireless access to an ATM backbone network. We derive expressions for the PCS-to-PCS, PCS-to-wireline and wireline-to-PCS call setup delays. These expressions are functions of utilization and of the delays to authenticate a PCS user, process a signaling message, and set up an ATM connection, among others. Numerical results are presented for wide ranges of parameter values. The impact of various parameters on these results is studied. It is found that the delay to authenticate a PCS user is a major component of call setup delay for the studied parameters. Reducing the authentication delay from 500 to 100 ms decreases the call setup delay between 10 and 50%.

An asymmetric air interface protocol is one which allocates more capacity for one direction of data transfer (in our case, the downlink) than the other. In this paper we report ongoing work on the need and initial design calculations for an asymmetric indoor air interface protocol which is suitable for integrated voice and data applications, and specifically for wireless Internet access. As an example we consider PACS-UB, a symmetric protocol for voice communication in the isochronous unlicensed PCS band (1920-1930 MHz), and present a mechanism for making it statically asymmetric, as well as dynamically asymmetric in response to traffic demands. We also present a simplified worst-case two-dimensional model of co-channel interference when the air interface protocol is dynamically asymmetric. The quantitative results of the model indicate that an asymmetric protocol can result in significant gains in spectral efficiency. In the worst case downlink co-channel interference can be significant, and we discuss possible mitigating techniques that could be used.

There is a growing interest in the research community in mechanisms that transport asynchronous transfer mode (ATM) cells over a wireless link (wireless-ATM), and in wireless access to ATM backbone networks (broadband wireless networking). This paper presents an architecture for broadband wireless networking that supports PCS (personal communication services) using an ATM backbone. We develop analytical and simulation models to measure the delay of PCS registration and call delivery. The performance models are illustrated with numerical examples that reveal the high sensitivity to the processing speed of network entities. Their agreement provides a first cut engineering approximation that can easily be applied to other networks and systems.

Current cellular subscribers have a geographic phone number (e.g., in AMPS and US digital cellular systems) or a number which contains the network provider's identity (e.g., in GSM), and whenever subscribers register or receive (and possibly, originate) a call, a home location register (HLR) database has to be queried. The wired infrastructure supports a function called global title translation (GTT) that converts the subscriber's number to an HLR database address. A special feature of next generation wireless access service will be to support personal communication services (PCS) and wireless subscribers with portable personal numbers, or nongeographic phone numbers (NGPNs), that do not indicate the service provider or HLR database serving the user. In addition, the GTT function may not be available when the wired backbone is an ATM network. Thus a key function required in future wireless access systems with wired ATM backbones will be the ability to translate an NGPN to the identity of the HLR which serves the subscriber, a process we call NGPN translation. We discuss the requirements of NGPN translation and some alternative schemes. We propose two schemes for fast, efficient, scalable and flexible NGPN translation which use ideas of dynamic hashing, caching, and indirection. The schemes use a hash function in the visiting location registers (VLRs) (or serving SCP) and a set of distributed translation servers which store the NGPN-to-HLR mapping. We discuss how the operations required to maintain the translation information can be performed. Finally, we perform a simplified analysis of the scalability of the alternative schemes as well as the hash-based schemes we propose.

System capacity of PACS (personal access communications system) is determined by two factors: (1) blocking due to insufficient servers at the radio port being accessed and (2) blocking due to insufficient signal quality of the radio link being accessed. The Erlang traffic capacity can be enhanced by access re-routing, i.e., a user is allowed to access other available radio ports immediately if it fails in a previous attempt. However, the signal quality would be degraded due to re-routing if the cell size is relatively large. The signal quality performance can be improved by reducing the cell size but the cell size cannot be too small for economic and technical reasons. This study is to investigate the effects of both cell size reduction and access re-routing on the overall system performance of PACS and to examine the tradeoffs between different system parameters. It is found that with cell size reduction and access re-routing together, the overall system performance is greatly improved. At a reasonably high normalized offered traffic of 60%, the overall call blocking probability is reduced from 11.5% to 3.5% by changing a port-to-port separation of 2000 ft. (i.e., a cell radius of 1000 ft.) without re-routing to 1000 ft. with re-routing. A number of 3 or 4 re-routing attempts out of a maximum of 16 is sufficient to provide a good result. In addition, more than 90% of the successful calls are admitted in the first attempt and therefore, the additional access delay and system overhead due to re-routing is insignificant.

Current cellular subscribers have a geographic phone number (e.g. in AMPS and US digital cellular systems) or a number which contains the network provider's identity (e.g. in GSM), and whenever subscribers register or receive (and possibly, originate) a call, a home location register (HLR) database has to be queried. A special feature of next generation wireless access service will be to support PCS and wireless subscribers with portable personal numbers, or non-geographic phone numbers (NGPN), that do not indicate the service provider or HLR database serving the user. In addition the global title translation (GTT) function that converts the subscriber's number to an HLR database address may not be available when the wired backbone is an ATM network. Thus a key function required will be to translate an NGPN to the ID of the HLR which serves the subscriber, a process we call NGPN translation. (Note that the same functionality is also needed for subscribers with local, portable phone numbers.) We discuss the requirements of NGPN translation and some alternative schemes. We propose a scheme for fast, efficient, scalable and flexible NGPN translation which applies ideas of dynamic hashing, caching, and indirection. The scheme uses a hash function in the visiting location registers (VLR) (or serving SCP) and a set of distributed translation servers which store the NGPN-to-HLR mapping.

The FCC has allocated the band between 1920 MHz and 1930 MHz for unlicensed personal communications services (UPCS) using isochronous or circuit operation. The UPCS spectrum is between the licensed PCS spectrum bands of 1850-1910 MHz and 1930-1990 MHz. Terminal interoperability in both the UPCS spectrum on private indoor wireless systems and the licensed spectrum on public PCS systems is desirable and encouraged by the FCC. This paper presents a port channel assignment process for the personal access communications system-unlicensed B (PACS-UB) which abides by the FCC etiquette for UPCS and discusses the corresponding uplink and downlink performance. Uplink power control is employed to improve the uplink performance. PACS-UB has a high degree of commonality with licensed PACS to permit economical licensed/unlicensed terminals and common network services. The results of our simulation show that, at 1% to 2% blocking probability, 99% of downlink local-mean signal-to-noise plus interference ratio (SINR) values are above 17 dB for a 10 to 20 m port separation. For a three-dimensional office environment, the uplink limits the SINR performance, however, with uplink power control, a 5.5 to 7 dB improvement in the uplink SINR can be achieved even for high traffic load.

The FCC has allocated the spectrum between 1850-1910 and 1930-1990 MHz for licensed personal communications services (PCS) and the band between 1920-1930 MHz for unlicensed PCS (UPCS). This paper describes a polling deregistration protocol for a wireless access communications network which would support interoperability between licensed personal communications services (PCS) and unlicensed-PCS (UPCS). We show how the protocol can be efficiently implemented in the personal access communications system (PACS) for licensed PCS and in the PACS-Unlicensed Version B (PACS-UB). An analytical model is proposed to analyze the performance of the polling protocol. A cost function is derived, which can be used to estimate the optimal polling frequency.

For CDMA (code-division multiple-access) wireless communications systems, orthogonal signaling with noncoherent detection has been proposed when a reference phase is not available. In this paper, orthogonal signaling using Walsh signals is considered. Performance of the channel using error-correcting coding together with 1) bit-by-bit interleaving or 2) Walsh word-by-word interleaving is investigated. Simulation results show that for several types of fading and non-fading channels with practical amounts of interleaving and with practical power control, the second technique with complete soft decision decoding that has added complexity in the decoder gives significant reduction in the required signal to interference ratio (SIR) over the first technique.>

This paper discusses the performance of a slow-frequency-hopped time-division multiple access (SFH-TDMA) technique, which can be considered as a "high-tier" extension of a low-complexity TDMA architecture optimized for low-power pedestrian applications. A hard-limited receiver is employed and a novel weighting factor for diversity combining is developed to achieve an effect similar to that of a maximal ratio combiner. Numerical performance results for frequency-selective fading channels over a range of fading rates were obtained through computer simulations.

Public-key/private-key hybrid key agreements and authentication protocols which maintain privacy of conversation and location information, and deter usage fraud, are presented. These protocols are optimized for low complexity in the portable unit and network infrastructure. The basic cryptographic techniques are described, and some complexity information obtained from these laboratory experiments and from other sources are presented. The three public-key protocols described have differing levels of security and complexity: and the tradeoffs are discussed. Because of the complexity concerns mentioned above, the public-key protocols are compared to a representative private-key approach in the areas of both security and computational complexity.>

Power control is essential in the use of direct-sequence code-division multiple-access (CDMA) techniques over fading radio channels. The paper investigates a feedback power control approach that allows power commands to be updated at a higher rate than the rate of multipath fading. The signal and interference statistics as received at the base stations after power control are obtained for a simulated CDMA system which includes multiple base stations with diversity receivers and a large number of power-controlled users continuously moving at various speeds. The authors show that often-used analyses based on perfect average power control lead to optimistic capacity results (by about 25%) because interference is underestimated by as much as 1 dB.>

A combined burst synchronization and error detection scheme is studied for a time-division multiple access (TDMA) portable radio system. Analysis, computer simulation, and experimental results of the false acceptance rate of the system using the combined scheme are presented. It is found that for a (161,147) code used in this study, which is capable of correcting +or-6-b sync slippage, the error detection capability of the code is degraded by 3 b on a slow Rayleigh fading channel using coherent QPSK demodulation with differential decoding. However, lower implementation complexity and higher efficiency are obtained than with separate burst synchronization and error detection processes.>

It is expected that personal communications services (PCSs) will provide access to the wireline telephone network for a large number of telephone calls via low-power, portable, digital radio telephones. The use of radio makes such a PCS more susceptible to eavesdropping than are conversations carried via wires. The mobility of PCS users also presents new problems relating to 1) authentication-ensuring service is not obtained fraudulently, and 2) the privacy of information about the PCS user's location. It is important that PCSs provide privacy (of conversation and location) and fraud control comparable to that of the wireline network. The paper compares two approaches to providing privacy and authentication for PCSs: a conventional approach using "private-key" cryptographic technology, and a new approach using "public-key" technology. It is concluded that the public-key approach provides superior security while maintaining comparable call set-up performance.>

It is shown that the degradation in the performance of wideband digital transmission systems due to intersymbol interference can be reduced by utilizing diversity selection using coding. A BCH (31, 21, 5) double-error-correcting code and QPSK (quadrature-phase-shift-keying) modulation with coherent detection are used for this study. The probability of word error is taken to be the measure of system performance. Analytic expressions are derived for the word error probability; these expressions simplify the simulation processes. It is found that a diversity selection algorithm using coding can reduce the floor of word error probability, and hence increase the dynamic range of received power before the word error probability reaches that floor.>