Sung Ho Moon

Capacity improvement in CDMA downlink with orthogonal code-hopping multiplexing

Orthogonal code-hopping multiplexing (OCHM) is a statistical multiplexing scheme designed to increase the number of allowable downlink channels in code division multiple access (CDMA) systems. OCHM is expected to compensate for a lack of codewords in future communication systems. In CDMA systems including OCHM, system capacity is limited by the number of codewords and power (or interference), and the maximum system capacity is determined by a stronger limitation between them. Call blockings due to power limitation may occur firstly if downlink channels demand large E/sub b//I/sub 0/ values and a high-channel activity. On the other hand, code limitation may occur prior to power limitation in CDMA. The maximum system capacities determined by both code and power limitations must be known, even in OCHM. However, previous studies on OCHM system capacity focused only on increasing the number of multiplexed users with no consideration of the power limitation. In this paper, the overall system capacity of OCHM considering both code and power limitations was evaluated. For this analysis, the transmission chip energy of base station (BS) and inner/outer-cell interference is mathematically derived in a multicell and multiuser environment. The downlink system capacity for OCHM is larger than for orthogonal code division multiplexing (OCDM) as other cell interference (OCI), mean channel activity, and the required E/sub b//I/sub 0/ value decrease.

Orthogonal code hopping multiplexing for downlink statistical multiplexing

For orthogonal downlink and statistical multiplexing, three modes of orthogonal code hopping multiplexing (OCHM) are proposed to accommodate more orthogonal downlink channels than orthogonal codewords for downlink channels, and they are compared. The performance comparison shows that the hybrid mode OCHM outperforms both the division mode and the hopping mode.

Multi-QoS scheduling algorithm for class fairness in high speed downlink packet access

Since there are various packet-type services with different QoSs , a scheduling algorithm that can support multiple QoS classes is needed to efficiently provide data services in the high speed downlink packet access (HSDPA). In this paper, we investigate the capability of HSDPA to support multiple QoS classes and propose an improved scheduling algorithm to serve multiple QoS classes

Frame level control for collision mitigation in orthogonal code hopping multiplexing

We have recently proposed an orthogonal code hopping multiplexing (OCHM) scheme which is based on a statistical multiplexing scheme for orthogonal downlink in direct sequence spread spectrum systems. This is a feasible candidate for accommodating a large number of bursty packet-based users with good backward compatibility. In OCHM, code-collisions which degrade channel coding performance and result in an increase in the required E/sub b//N/sub 0/ are inevitable for obtaining a statistical multiplexing gain. In this paper, we lower code-collision probability by discarding or delaying excessive frames whose number is larger than a threshold value. It reduces the required E/sub b//N/sub 0/ at the transmitter and saves system power. However, there is an increase in BLER (block error rate) or delay. Therefore, there exist trade-offs between the required E/sub b//N/sub 0/ and BLER (or delay). We can determine an operating point which can reduce the required E/sub b//N/sub 0/ by considering how much BLER or delay the system requires as a target value.

Hybrid scheduling scheme for a cooperative relay system in heterogeneous traffic environments

We propose a hybrid scheduling scheme which can efficiently support various types of traffic in a cooperative relay system of downlink cellular networks. The hybrid scheduling scheme harmonizes the shared-channel resource allocation scheme and dedicated-channel resource allocation scheme to accommodate various traffic in heterogeneous traffic environments. We show that the proposed scheme significantly improves the system performance in terms of system throughput in heterogeneous traffic environments through the analysis of the system capacity and throughput.

Group-Mode Hopping for Collision Mitigation in Orthogonal Code-Hopping Multiplexing

Orthogonal code-hopping multiplexing (OCHM) is a statistical multiplexing scheme designed to increase the number of allowable downlink channels in code-division multiple-access (CDMA) systems. OCHM makes it possible to use orthogonal code resources more efficiently than the conventional dedicated codeword allocation/multiplexing schemes in CDMA2000 and wideband CDMA (WCDMA) systems. Collision-allowable hopping in the OCHM system yields a statistical multiplexing gain. However, collisions may degrade the bit error rate (BER) performance. A group-mode hopping scheme is proposed as a collision mitigation scheme for OCHM. The performance of the proposed scheme is evaluated using numerical analysis and simulations.

1/spl times/EV-DO system-level simulator based on measured link-level data

1/spl times/EV-DO systems are being deployed widely for high speed wireless data communications. A 1/spl times/EV-DO system-level simulator is developed to evaluate the forward link capacity in an environment of multi-cell, multi-user, and mixed traffic of HTTP, FTP, NRV, and WAP, using measured link-level data, such as data rate transition thresholds and FER from HPEOS (high rate packet data performance evaluation and optimization system for cdma2000 1/spl times/EV-DO). The performance of the 1/spl times/EV-DO system is evaluated in terms of utilization, service throughput, over-the-air (OTA) throughput, and packet delay for four different traffic types, by using the system-level simulator.

System-level simulator for the W-CDMA low chip rate TDD system

A system-level simulator for the W-CDMA low chip rate TDD system is developed. This simulator considers multi-cell and multi-user environments and SIR-based power control. For accurate and reliable results, inner-cell and outer-cell interference is modeled by chip-level spreading and an SIR estimation scheme is used. From this simulator, system-level performance is evaluated in terms of the received SIR distributions for downlink and uplink. The degradation probability is also introduced as a QoS indicator at system level.

Throughput Estimation of Downlink Packet Access Systems Based on a Point Mass Approximation Concept

Although the system throughput of a wireless communication system considering multiple users geographical distribution on a 2-D plane and various traffic characteristics is an important performance metric, its mathematical analysis is very difficult due to the nonindependent identically distributed distribution of the received signal-to-noise ratio (SNR) of each mobile terminal and the complex dynamics of the traffic patterns. Therefore, complicated system-level simulations have been the only approach to evaluate the system throughput of downlink packet-access systems. In this paper, we propose an efficient analytical approach to estimate the system throughput of downlink packet-access systems by using point mass approximation, which is widely used in physics and mechanics. The proposed analysis framework enables the mathematical analysis of the system throughput performance by considering various positions of mobile terminals and traffic patterns without the complicated and heavy system-level simulations. Although the proposed approach has a tradeoff relation between computation complexity and accuracy, we show that it is possible to obtain an effective accuracy with moderate complexity using the proposed analytical approach.

Distance-Based Code-Collision Control Scheme Using Erasure Decoding in Orthogonal Code Hopping Multiplexing

Orthogonal code hopping multiplexing (OCHM) was developed to accommodate more downlink orthogonal channels than the number of orthogonal codewords through statistical multiplexing. Therefore, code-collisions may occur due to random code hopping patterns. The conventional code-collision control schemes are synergy and perforation. We propose a distance-based code-collision control scheme using erasure decoding in OCHM. The proposed scheme utilizes the conventional synergy scheme when all of the code-colliding symbols are identical. However, a base station (BS) selects a symbol which the nearest mobile station (MS) among code-colliding MSs wants to receive and transmits it with the controlled signal level in downlink when any of the code-colliding symbols is different from others. This scheme yields better performance at the nearest MS from BS among code-colliding MSs. MSs except the nearest MS receive the symbol with much smaller amplitudes due to different path losses. These smaller signal amplitudes are erased by an erasure decoding scheme at the receiver. Therefore, the performance of MSs except the nearest MS is not degraded, compared with that of the conventional perforation scheme.