Myeon-Gyun Cho

Performance Analysis of Reuse-Partitioning-Based Subchannelized OFDMA Uplink Systems in Multicell Environments

This paper presents a performance analysis of reuse partitioning (RUP)-based subchannelized orthogonal frequency-division multiple-access (OFDMA) uplink systems in multicell environments. The cochannel interference (CCI) statistic is calculated for OFDMA uplink systems. The derived statistic is then used to analyze the performance of subchannelized OFDMA systems based on RUP. Analysis and simulation results show that the performance of a subchannelized OFDMA system in multicell environments is noticeably dependent on the CCI, and the effect of CCI can be reduced by the RUP scheme. Finally, the results of the analysis yield the optimum RUP area for achieving the maximum system throughput.

A joint feedback reduction scheme using delta modulation for dynamic channel allocation in OFDMA systems

A novel feedback reduction scheme is proposed for dynamic channel allocation (DCA) in OFDMA systems. Applying this delta-modulation (DM)-based scheme to the channel gain of adjacent subcarriers reduces the feedback information to 1 bit per subcarrier. Since this reduced feedback information can lead to performance degradation in a bit error rate (BER), a modified amplitude craving greedy (ACG) method and improved DM are jointly adopted to minimize the loss. Simulation results verify that the proposed scheme can decrease feedback information by a factor of 1/M while retaining performance comparable to the full feedback case, which requires M bits per subcarrier

On the optimal number of hops in linear wireless ad hoc networks with hybrid ARQ

In this paper, we study the optimal design of a linear wireless multihop network that employs Hybrid Automatic Repeat reQuest (HARQ) protocols in a quasi-static fading environment. Data transmission is assumed to be delay-tolerant up to a certain predefined maximum delay (in transmission slots) that is larger or equal to the number of hops. Multihop routing is implemented through a time-division scheduling and decode-and-forward relaying. Excess time is exploited for retransmissions using either HARQ Type I or Chase Combining protocols on the hops that result in link-outage. Relying on analysis and numerical optimization, we seek answer to the following question: given the maximum allowed delay and signal-to-noise ratio, what is the optimal number of hops that maximizes the end-to-end throughput?

Performance Analysis of Dynamic Channel Allocation Based on Reuse Partitioning in Multi-Cell OFDMA Uplink Systems*This paper was presented on Poster 3: Communications (1) section at the ITC-CSCC 2005.

Our investigation is presented into analysis of the co-channel interference (CCI) statistic in orthogonal frequency-division multiple access (OFDMA) uplink systems. The derived statistic is then used to analyze the performance of reuse partitioning (RP)-based dynamic channel allocation (DCA). Analysis and simulation results show that the performance of DCA in multi-cell environments is noticeably dependent on the CCI. Finally, the results of the analysis yield the optimum RP area for achieving the maximum spectral efficiency.

A CQI Feedback Reduction Scheme for Multi-User MIMO/OFDMA Systems

An opportunistic scheduling is adopted to improve the capacity of the system by exploiting the multiuser diversity of multiuser MIMO (MU-MIMO)systems. However, it requires a large amount of feedback carrying the channel quality information (CQI) of each user to the transmitter. The considered per user unitary and rate control (PU2RC) needs to feedback the preferred precoding index and its CQIs, and it has a defect in scheduling the streams for the grouped user. In order to overcome these drawbacks, a novel feedback reduction scheme is proposed and is modified for OFDMA systems in this paper. It employs transmitter controlled precoding and opportunistic feedback (TCP-OFB) in conjunction with frequency scheduling. The simulation results demonstrate that TCP-OFB/OFDMA shows comparable performance to PU2RC while it only requires far reduced feedback load.

A novel time spreading method for down-link OFDM-code division multiplexing systems

Orthogonal frequency division multiplexing code division multiplexing (OFDM-CDM) using a novel time spreading scheme is proposed as an alternative to multicarrier code division multiple access (MC-CDMA) systems. A residual frequency diversity gain can he fully obtained with OFDM-CDM through the adaptation of the proposed time spreading scheme which has a known frequency-hopping pattern over the whole transmission bandwidth. If there is enough frequency space to hop and the space is larger than the coherent bandwidth of the channel, we can exploit full frequency diversity in any channel environment. Simulation results verify that the proposed method achieves a gain of about 4 dB for BER of 10/sup -3/ compared to the conventional OFDM-CDM, which achieves a similar performance as frequency-interleaved MC-CDMA.

An Efficient CQI Feedback Scheme for Multiuser MIMO Systems

An opportunistic scheduling is adopted to improve the capacity of the system by exploiting the multiuser diversity of multiuser MIMO (MU-MIMO) systems. However, it requires a large amount of feedback carrying the channel quality information (CQI) of each user to the transmitter. The considered per user unitary and rate control (PU2RC) needs to feedback the preferred preceding index and its CQIs, and it has a defect in scheduling the streams for the grouped user. In order to overcome these drawbacks, a novel feedback reduction scheme is proposed and is modified for OFDMA systems in this paper. It employs transmitter controlled preceding and opportunistic feedback (TCP-OFB) in conjunction with frequency scheduling. The simulation results demonstrate that TCP-OFB/OFDMA shows comparable performance to PU2RC while it only requires far reduced feedback load.

A New Full-band Feedback Scheme Using the Adaptive Grouping Method in OFDMA Systems

Opportunistic scheduling algorithms with link adaptation can increase system throughput, but have the drawback of requiring the channel quality information (CQI) to be transmitted from all the candidate users. In order to alleviate this problem, we propose a new feedback reduction scheme that preserves CQIs over all channels. The proposed scheme binds similar CQIs in groups to represent them more effectively, and uses a simple method for fast grouping. Simulation results show that the proposed scheme with this simple grouping achieves close to perfect feedback performance with respect to the original CQIs under reasonable feedback loads.

Synchronization Performance Comparison between Adaptive Filter and Correlator

In this paper, we compare the timing synchronization performance of the adaptive filter to that of the correlator in direct sequence spread spectrum (DS/SS) systems. The test variables used in the code synchronization are statistically analyzed for both schemes, and then the obtained results are used in calculating the detection and false alarm probabilities. Based on the derived probabilities, the synchronization performance is compared and the simulation is followed. Analysis and simulation results show that the correlator outperforms the adaptive filter under most acquisition environments.

A Novel 2-Dimensional Spreading Method for Down-Link OFDM-Code Division Multiplexing Systems

In this letter, orthogonal frequency division multiplexing-code division multiplexing (OFDM-CDM) using a novel 2-dimensional spreading scheme is proposed as a candidate for a next-generation multiple access scheme. Full residual frequency diversity gain can be obtained with OFDM-CDM by adapting the proposed 2-dimensional spreading scheme with a novel frequency-hopping technique. Setting the frequency-hopping pattern in proper consideration of the coherent channel bandwidth allows us to exploit both the full frequency diversity and the time diversity in any channel environment.