High-speed Packet Data Services Research Articles

A data flow optimization method for high speed MAC processing in an IEEE 802.16m modem

IEEE 802.16m technology is expected to provide high speed packet data service over wireless. Due to the large amount of data to be processed over a short period of time, an efficient MAC processing in the modem is crucial. Since the MAC processing algorithm has optimization limitations, we focus on a data flow optimization in the system level design, so that the number of external memory accesses is minimized. Experimental results show that our approach results in an up to sixteen times faster IEEE 802.16m modem system.

Transmit Diversity Schemes for BCH Transmission in IEEE 802.16m

IEEE802.16m standard is based on the MIMO-OFDM technology to provide high speed packet data service both in downlink and uplink. For the downlink broadcasting of control information, in order to extend the coverage of a cell, the nominal operating point should be set for the user at the edge of a cell, and no feedback should be used. For broadcasting that information, the MIMO technology should take a transmit diversity form targeted for low SNR. Several transmit diversity schemes are presented and preferable modes of operations for the broadcasting channel are proposed with numerical analysis.

Combined Effect of Random Transmit Power Control and Inter-Path Interference Cancellation on DS-CDMA Packet Mobile Communications

In mobile communication systems, high speed packet data services are demanded. In the high speed data transmission, throughput degrades severely due to severe inter-path interference (IPI). Recently, we proposed a random transmit power control (TPC) to increase the uplink throughput of DS-CDMA packet mobile communications. In this paper, we apply IPI cancellation in addition to the random TPC. We derive the numerical expression of the received signal-to-interference plus noise power ratio (SINR) and introduce IPI cancellation factor. We also derive the numerical expression of system throughput when IPI is cancelled ideally to compare with the Monte Carlo numerically evaluated system throughput. Then we evaluate, by Monte-Carlo numerical computation method, the combined effect of random TPC and IPI cancellation on the uplink throughput of DS-CDMA packet mobile communications.

Coordinated load balancing, handoff/cell-site selection, and scheduling in multi-cell packet data systems

We investigate a wireless system of multiple cells, each having a downlink shared channel in support of high-speed packet data services. In practice, such a system consists of hierarchically organi...

Coordinated load balancing, handoff/cell-site selection, and scheduling in multi-cell packet data systems

We investigate a wireless system of multiple cells, each having a downlink shared channel in support of high-speed packet data services. In practice, such a system consists of hierarchically organized entities including a central server, Base Stations (BSs), and Mobile Stations (MSs). Our goal is to improve global resource utilization and reduce regional congestion given asymmetric arrivals and departures of mobile users, a goal requiring load balancing among multiple cells. For this purpose, we propose a scalable cross-layer framework to coordinate packet-level scheduling, call-level cell-site selection and handoff, and system-level cell coverage based on load, throughput, and channel measurements. In this framework, an opportunistic scheduling algorithm--the weighted Alpha-Rule--exploits the gain of multiuser diversity in each cell independently, trading aggregate (mean) down-link throughput for fairness and minimum rate guarantees among MSs. Each MS adapts to its channel dynamics and the load fluctuations in neighboring cells, in accordance with MSs' mobility or their arrival and departure, by initiating load-aware handoff and cell-site selection. The central server adjusts schedulers of all cells to coordinate their coverage by prompting cell breathing or distributed MS handoffs. Across the whole system, BSs and MSs constantly monitor their load, throughput, or channel quality in order to facilitate the overall system coordination. Our specific contributions in such a framework are highlighted by the minimum-rate guaranteed weighted Alpha-Rule scheduling, the load-aware MS handoff/cell-site selection, and the Media Access Control (MAC)-layer cell breathing. Our evaluations show that the proposed framework can improve global resource utilization and load balancing, resulting in a smaller blocking rate of MS arrivals without extra resources while the aggregate throughput remains roughly the same or improved at the hot-spots. Our simulation tests also show that the coordinated system is robust to dynamic load fluctuations and is scalable to both the system dimension and the size of MS population.

Physical-layer design for next-generation cellular wireless systems

The conventional cellular architecture will remain an integral part of next-generation wireless systems, providing high-speed packet data services directly to mobile users and also backhaul service for local area networks. In this paper, we present several proposals addressing the challenges associated with the critical design issues for the next-generation cellular wireless physical layer. These proposals include an orthogonal frequency division multiplexed (OFDM) or multicarrier code division multiple access (MC-CDMA) air interface for wide channel bandwidths, considerations for resource allocation, multiple antenna techniques, a hybrid duplexing technique combining the benefits of time division and frequency division duplexing, and coordinated networks for reducing intercell interference and increasing overall spectral efficiency.

Rate Scheduling in Multiple Antenna Downlink Wireless Systems

We consider scheduling strategies for multiantenna and multibeam cellular wireless systems for high-speed packet data services on the downlink. We establish a fundamental connection between the stability region of the queuing system and the set of feasible transmission rates, which provides the basis for the scheduling algorithm proposed in this paper. Transmission using adaptive steerable beams and fixed sector beams are considered and average delay versus throughput results are obtained through simulations for the proposed scheduling scheme in each case. While in single antenna systems multiuser diversity gains are achieved by the scheduling algorithms that transmit to a single user in each scheduling interval, our results show that with multiple antennas, transmitting to a carefully chosen subset of users has superior performance. The multiantenna scheduling problem is closely related to the problem of coordinated scheduling for transmission through multiple base stations, where a user can receive signals from several base stations simultaneously. We consider the special case when three single-antenna base stations are allowed to cooperate and transmit to the users in the triangular region between the base stations and propose scheduling strategies that demonstrate significant gains.

Optimizing the ARQ performance in downlink packet data systems with scheduling

Third generation wireless systems typically employ adaptive coding and modulation, scheduling, and Hybrid Automatic Repeat reQuest (HARQ) techniques to provide high-speed packet data service on the downlink. Two main considerations in designing such a system are algorithms for the selection of coding and modulation schemes based on the channel quality of the link and algorithms for the selection of the user to whom a particular slot is assigned. We propose a systematic approach to optimize the mapping between signal-to-interference-and-noise ratio (SINR) and modulation and coding scheme (MCS) to maximize the throughput by taking into account the type of HARQ scheme employed. We also propose to incorporate frame error rate (FER) and retransmission information as a part of the scheduling decision. The proposed scheduler ranking methods based on using an effective rate rather than the instantaneous rate provide natural priority to retransmissions over new transmissions, and priority to users with better channel quality. Extensive simulation results comparing performance of the proposed methods to conventional methods are presented.

Packet Scheduler for Mobile Internet Services Using High Speed Downlink Packet Access

Internet services are becoming essential in the third- and fourth-generation cellular mobile networks. In order to provide effectively the packet data service with scarce radio resource, several systems, including the High Speed Downlink Packet Access (HSDPA) enhancement of wideband code-division multiple access (WCDMA), have been proposed. In this paper, we design an Internet Protocol (IP) packet scheduler for high-speed packet data services using the wireless packet access system. We design the scheduler so that its performance is maximized from the standpoint of end-to-end application level rather than from the standpoint of radio interface. To do so, the scheduler aims at avoiding excessive packet delays that may invoke the slow-start on the Transmission Control Protocol (TCP) connections. The performance of the proposed scheme is evaluated by extensive simulation and compared with the performances of the existing three schedulers. The results show that the proposed scheduler has remarkably better performance than the baseline schedulers for performance comparison.

PERFORMANCE OF UMTS PACKET SERVICE OVER DEDICATED CHANNELS (DCH)

The provision of high speed packet data services in an efficient way is probably the most important challenge for the Universal Mobile Telecommunications System (UMTS) since this can give an advantage over second generation systems. The efficiency depends mainly on the radio interface due to its great flexibility. It is of utmost importance to investigate the effect of different configurations on the system performance. In this paper we evaluate the performance of packet data services over downlink dedicated channels (DCH) by means of detailed simulations. Due to the traffic variability, Automatic Repeat reQuest (ARQ) mechanism and closed loop power control the system behavior is quite complex and not so easily predictable as with constant rate services such as voice. We study the effect of several parameters (spreading factor, code rate, channel setup delay, etc.) on the system capacity by means of the delay-throughput curves. We show that the setting of parameters may be critical for system capacity and stability. For this reason we propose a flow control mechanism which is able to guarantee stability and enable the system capacity to be almost independent of channel rates.

Multiple antennas in cellular CDMA systems: transmission, detection, and spectral efficiency

Providing wireless high-speed packet data services for Web browsing and streaming multimedia applications will be a key feature in future code-division multiple-access (CDMA) systems. We study down-link CDMA schemes for providing such services using multiple antennas at the transmitter and receiver. We propose a generalization of the point-to-point narrowband Bell Labs layered space-time (BLAST) system to a wideband multiple access system which simultaneously supports multiple users through code spreading. We discuss transmission options for achieving transmit diversity and spatial separation and introduce a generalization of the vertical BLAST detector for CDMA signals. Using link level simulations, we determine the bit-error rates versus signal-to-interference ratio of the various transmitter options. We then describe a novel technique for determining the system spectral efficiency (measured in bits per second per Hertz per cell sector) by incorporating the link level results with system level outage simulations. Using four antennas at the transmitter and eight antennas at each receiver, the system can support multiple receivers at 16 times the voice rate, resulting in a system spectral efficiency an order magnitude higher than a conventional single-antenna voice system.

Enhanced random access and reservation scheme in CDMA2000

The growing demand for high-speed packet data services and multimedia applications over mobile personal communication networks has set new design requirements and objectives for the next generation of air interface protocols. The asymmetric and bursty nature of multimedia packet data traffic, and the variability of data rates, packet sizes, and quality of service requirements make conventional voice-oriented channelization and access protocols inefficient. New media access control and common channel messaging procedures need to be defined to efficiently support concurrent multiple packet- and circuit-switch-based services and their related signaling messages. Specifically, the role of common channels in support of frequent short packet data and signaling transactions is much more significant. This article presents the new enhanced random access and reservation schemes in CDMA2000 as well as related concepts considered in the design of the current and future releases of this air interface standard. The scheme is based on a variation of packet reservation multiple access combined with variable data rate, power control and soft handoff capabilities, formalized within wideband CDMA2000 framework.