Dong Geun Jeong

CDMA/TDD system for wireless multimedia services with traffic unbalance between uplink and downlink

This paper proposes a code division multiple access (CDMA) time division duplex (TDD) system for wireless multimedia services with traffic unbalance between uplink and downlink. In the proposed system, the number of uplink time slots in a TDD frame differs from that of downlink. Moreover, the difference can be reset by the network operator according to the traffic pattern. We evaluate the performance of the proposed system under multimedia environment using Markov analysis and computer simulation. The results show that the frequency utilization is maximized even when the uplink and downlink traffic volumes are unbalanced. This, in turn, reduces drastically the blocking rate of multimedia calls (connections) in the proposed system compared with that in the traditional CDMA systems where the uplink and downlink use equal bandwidth.

Performance of an exponential backoff scheme for slotted-ALOHA protocol in local wireless environment

Slotted ALOHA is widely used in local wireless communications not only by itself as a multiple access protocol but also as a component in many reservation protocols. The paper suggests a very simple backoff scheme for slotted ALOHA and evaluates its performance in local wireless environments. The authors analyze the system capacity in full load conditions and the throughput-delay characteristics in underload conditions. They conduct a computer simulation to evaluate the system performance in transient-state. They also give a protocol parameter value which is highly recommendable from the practical viewpoint. As an application example, they examine the packet reservation multiple access (PRMA) system with the suggested backoff scheme and compare its performance with that of the original PRMA system. >

Call admission control for CDMA mobile communications systems supporting multimedia services

The call admission control (CAC) belongs to the category of resource management. Since the radio spectrum is very scarce resource, CAC is one of the most important engineering issues for mobile communications. In this paper, we propose a CAC scheme for direct sequence code-division multiple-access cellular systems supporting mobile multimedia communications services. There are multiple call classes in multimedia services and the required signal-to-interference ratio (SIR) varies with call classes. Call admission decision in the proposed scheme is based on SIR measurement. We take account of the traffic asymmetry between uplink and downlink, which is the most important characteristic of multimedia traffic. In addition, the proposed scheme guarantees the priority of handoff call requests over new call requests. We evaluate the performance of the proposed scheme using Markov analysis. The performance measures which we focus on are the system throughput and the blocking probabilities of handoff calls and new calls. The outage probability of a call in progress is also calculated, which is the probability that the measured bit energy-to-noise density ratio of the call is smaller than the required value for maintaining adequate transmission quality. We present some numerical examples with practically meaningful parameter values and, as a result, show that the proposed CAC scheme can operate well in the mobile multimedia systems such as the International Mobile Telecommunications-2000 (IMT-2000) systems.

Energy-Efficient Channel Management Scheme for Cognitive Radio Sensor Networks

In designing a cognitive radio sensor network (CRSN), we need to take account of energy both efficiency and primary user (PU) protection since the CRSN consumes additional energy to support CR functionality such as channel sensing and switching, which can shorten the network lifetime. In this paper, we propose a new channel management scheme for CRSNs, which heightens the energy efficiency while not greatly disturbing a PU. The CRSN with the proposed scheme adaptively selects its operation mode among channel sensing, channel switching, and data transmission/reception, according to the channel-sensing outcome. Considering that the sensing outcome can be erroneous due to noise uncertainty, we design the proposed scheme on the basis of the partially observable Markov decision process framework. The simulation results show that the proposed scheme energy-efficiently operates while properly protecting a PU.

Sequential detection of cyclostationary signal for cognitive radio systems

The cyclostationary feature detector is a viable candidate for a primary user (PU) detection method of the cognitive radio (CR) system. However, it requires very long detection time, which leads to inefficient spectrum utilization. To reduce the detection time, we propose to apply the sequential detection framework to the cyclostationary feature detector. Unfortunately, a straightforward application cannot achieve a sufficient gain, which is expected with the sequential detection. To solve this problem, we design a novel detector, taking account of the cyclic phase of the cyclostationary signal. The simulation results show that the proposed detector reduces the average detection time almost in half. The proposed detector can well be applied to the CR systems that operate in the frequency bands, where the PUs have long interarrival and sojourn time. For example, the CR systems equipped with the proposed detector can efficiently exploit the white space in the VHF/UHF TV bands.

An efficient quiet period management scheme for cognitive radio systems

In cognitive radio (CR) systems, the channel sensing scheme for detecting the presence of primary user directly affects the quality-of-service of CR users and primary user. In this letter, we propose a sensing scheme that consists of a series of consecutive energy detections followed by feature detection, where the energy detection time is much shorter than the feature detection time. With the proposed scheme, multiple energy detections decrease the feature detection due to false alarm and the overall channel sensing time. The performance evaluation using Markov analysis shows that the proposed scheme can heighten the maximum channel utilization of CR users, while maintaining the detection delay of primary user under a predefined value.

Cross-layer Design of Packet Scheduling and Resource Allocation in OFDMA Wireless Multimedia Networks

We investigate the cross-layer design for the packet scheduling and resource allocation in the orthogonal frequency division multiple access (OFDMA) wireless networks. Our focus is the efficiency of the resource management scheme from the practical point of view. For physical (PHY) layer, an efficient resource allocation algorithm with low computational complexity is proposed to cope with the frequency selective fading. A packet scheduler at medium access control (MAC) is also designed in order to utilize the properties of packet data system. The resource allocator and the scheduler are tightly coupled together through the cross-layer approach. The simulation results show that the proposed scheme utilizes the resources effectively while guaranteeing the quality of service (QoS)

Two-Stage Semi-Distributed Resource Management for Device-to-Device Communication in Cellular Networks

In cellular networks, the device-to-device (D2D) communication increases the network capacity by spatial reuse of radio resources and prolongs the battery life of devices by reducing the transmission power. In this paper, we propose a two-stage semi-distributed resource management framework for the D2D communication. At the first stage of the framework, the base station (BS) allocates resource blocks (RBs) to BS-to-user device (B2D) links and D2D links, in a centralized manner. At the second stage, the BS schedules the transmission using the RBs allocated to B2D links, while the primary user device of each D2D link carries out link adaptation on the RBs allocated to the D2D link, in a distributed fashion. The proposed framework has the advantages of both centralized and distributed design approaches, i.e., high network capacity and low control/computational overhead, respectively. We formulate the problems of RB allocation to maximize the radio resources efficiency, taking account of two different policies on the spatial reuse of RBs. To solve these problems, we suggest a greedy algorithm and a column generation-based algorithm. By simulation, it is shown that the proposed scheme achieves the near-optimal performance while reducing the control/computational overhead.

Resource allocation scheme for device-to-device communication for maximizing spatial reuse

Recently, device-to-device (D2D) communication in cellular networks has gained much attention for enabling a base station (BS) to offload traffic to direct D2D links and for facilitating new network services. In this paper, we propose a semi-distributed resource allocation scheme for the D2D communication where the BS allocates radio resources for cellular user links and D2D links in a centralized manner while the modulation and coding scheme (MCS) level and the transmission power of D2D links are distributively decided by the device of each D2D link. We first formulate a resource allocation problem of which the objective is to maximize the spatial reuse of radio resources by allowing the simultaneous transmission of D2D links on the same resources. To solve the problem, we present a suboptimal greedy algorithm. By simulation, we show that the cellular networks with the proposed scheme achieve a higher network throughput by maximizing the spatial reuse of radio resources.

Design and performance evaluation of a new medium access control protocol for local wireless data communications

This paper proposes a new medium access control protocol for wireless data communications in local area, called the reservation-based multiple access with variable frame length (RMAV). We design RMAV under the consideration that the population of wireless terminals and the system load frequently change and are almost unpredictable in wireless data communications. RMAV is based on the slot reservation scheme and adopts a frame structure with variable length. The frame length increases as the number of active terminals and/or the system load increases. We evaluate the performance of RMAV by analysis and computer simulation. Due to its adaptability to traffic patterns, RMAV offers short delay in light load conditions and high throughput in heavy load conditions.