Jaewoo So

Performance Analysis of VoIP Services in the IEEE 802.16e OFDMA System With Inband Signaling

Although the voice over Internet protocol (VoIP) service is expected to be widely supported in wireless mobile networks, the feasibility and capacity of the protocol have not previously been studied in relation to the emerging IEEE 802.16e orthogonal frequency-division multiple access (OFDMA) system. Informing subscriber stations about new downlink or uplink resource assignments creates a signaling overhead that influences the system throughput. In particular, the performance of VoIP services is seriously affected by the signaling overhead because the symmetry between the downlink and uplink causes immense downlink overheads. However, previous research on the IEEE 802.16e OFDMA system has not taken the signaling overhead into consideration. In the analytical model presented here, the signaling overhead is considered in the evaluation of the uplink and downlink performance of VoIP services in the IEEE 802.16e OFDMA system.

Analysis of Cognitive Radio Networks with Channel Aggregation

This paper presents two channel aggregation schemes for wideband cognitive radio networks: a constant channel aggregation scheme and a variable channel aggregation scheme. In the variable channel aggregation scheme, the bandwidth of the cognitive user is aggregated with a probability distribution or aggregated on the basis of the number of the residual channels. These channel aggregation schemes are analyzed by using a Markov chain and are evaluated in terms of the throughput, the blocking probability, and the forced termination probability. Numerical and simulation results show that the variable channel aggregation scheme based on the residual channel improves the throughput of the cognitive users.

Performance analysis of DS/SSMA unslotted ALOHA system with variable length data traffic

We analyze the throughput of a direct-sequence spread spectrum multiple access (DS/SSMA) unslotted ALOHA system with variable length data traffic. The system is analyzed for two cases: (1) systems without a channel load sensing protocol (CLSP) and (2) systems with a CLSP. The bit-error probability and the throughput are obtained as a function of the signal-to-noise ratio (SNR) during message transmission, considering the number of overlapped messages and the amount of time overlap. We assume that the generation of data messages is Poisson distributed and that the messages are divided into packets before transmission. The system is modeled as a Markov chain under the assumption that the number of packets in a message is geometrically distributed with a constant packet length. The throughput variance of the DS/SSMA unslotted ALOHA system with variable length data traffic is obtained as the Reed-Solomon code rate varies. Results show that a significant throughput improvement can be obtained by using an error-correcting code.

Access scheme for integrated voice/data transmissions over common packet channel in 3GPP

In this letter, we propose a flexible channel assignment scheme using preemption as an access method for integrated voice/data transmissions over common packet channel (CPCH) in 3GPP. We analyze the proposed scheme and compare the performance of the proposed scheme with the performance of the basic, channel monitoring, and channel assignment schemes in view of the voice packet dropping probability and the average delay of data packet.

Feedback reduction scheme for downlink multiuser diversity

A group random access-based feedback scheme is proposed for multiuser diversity systems, where users are divided into several feedback groups according to their measured channel states. Different random access probabilities and number of feedback minislots are assigned to each feedback group. Each user competes to send a feedback message through random access if its scheduling metric exceeds a threshold. The base station jointly controls the random access probabilities, the thresholds, and the number of feedback minislots to adjust the feedback load. The proposed feedback scheme shows a good system capacity with limited feedback resources regardless of the number of users.

A Downlink Performance Analysis of VoIP Services Over an IEEE 802.16e OFDMA System

The voice-over-Internet protocol (VoIP) service is expected to be widely supported in wireless mobile networks, though its feasibility and capacity have not been studied in relation to the emerging IEEE 802.16e orthogonal frequency division multiple access (OFDMA) system. Using analytical and simulation models that we developed, we present the downlink performance of VoIP services over an IEEE 802.16e OFDMA system

Capacity and Fairness in Multiuser Diversity Systems with Opportunistic Feedback

An opportunistic feedback protocol is proposed for multiuser diversity systems with proportional fair scheduling and maximum-throughput scheduling. The uplink feedback period is divided into two subperiods and users randomly access the feedback minislots according to their scheduling metric. An integrated analytical model is developed for evaluating the proposed feedback protocol.

Performance analysis of a DS/SSMA unslotted ALOHA system with two user classes

In this paper, we propose a direct-sequence spread spectrum multiple access (DS/SSMA) unslotted ALOHA system with two user classes and analyze the throughput of the proposed system. Mobile stations (MSs) are divided into two classes according to priority or traffic characteristics such as delay-intolerant and delay-tolerant. Different permission probabilities are assigned to each class so that the appropriate quality of service can be provided. We assume that the generation of class 1 and 2 messages are Poisson distributed and the message is divided into several packets before transmission. The system is modeled as a two-dimensional Markov chain under the assumption that the number of packets transmitted immediately by both user classes is geometrically distributed and the packet length is constant. We calculate the packet success probability and the throughput as a function of the signal-to-noise ratio (SNR) during packet transmission, considering the number of overlapped class 1 and 2 messages and the amount of their time overlap. Moreover, we show that the proposed system differentiates user messages according to class and maintains a high throughput even under heavy traffic conditions using access control based on the channel load.

Adaptive traffic prediction based access control in wireless CDMA systems supporting integrated voice/data/video services

An access control protocol is proposed for integrated voice/data/video code-division multiple-access (CDMA) systems. The protocol involves predicting the residual capacity available for non-real-time data services in reverse link (mobile to base station). Two estimation schemes, a static estimation scheme and a dynamic estimation scheme, are proposed for predicting the residual capacity, the number or the data rate of data packets that could be scheduled at the next time slot. The performances of the proposed estimation schemes are evaluated in view of the outage probability and the mean data message delay.

Joint Proportional Fair Scheduling for Uplink and Downlink in Wireless Networks

Since many users share limited wireless resources in wireless networks, it is important for resources to be allocated among users in a fair and efficient manner. The scheduler at the base station is responsible for allocating resources to users. Many researchers have developed efficient scheduling algorithms but most these algorithms were designed separately and independently for the uplink or downlink. Because a user generally has two communication links, an uplink and a downlink, the overall satisfaction with a communication service can be formulated as the sum of the quality of the uplink and downlink services. Hence, the poor quality of either link can degrade the overall quality of service. This paper proposes a joint proportional fair (PF) scheduling algorithm for wireless networks, where the scheduling of the uplink and downlink is done jointly so that the bandwidth can be shared efficiently and fairly between the uplink and the downlink. The paper introduces three joint scheduling algorithms: joint delay-based scheduling, joint maximum rate scheduling, and joint PF scheduling. The simulation results show that in comparison with conventional scheduling algorithms the proposed joint PF scheduling algorithm achieves a better compromise between the throughput and user fairness by adjusting the weighting factor between the uplink and downlink.