Ilmu Byun

Delay-Constrained Random Access Transport Capacity

In this paper, we consider delay-constrained wireless multi-hop ad hoc networks where a packet should be delivered to the destination within the maximum allowed delay while satisfying the target outage probability. The proposed performance metric for analyzing networks is the delay-constrained random access transport capacity (D-RATC), which quantifies the maximum end-to-end (e2e) link achievable rate per unit area of a delay-constrained network using a random access protocol. The scaling of the D-RATC is obtained for various slotted ALOHA (SA) protocols and it is shown that the SA protocol is order-optimal for delay-constrained random networks when interference control is used with an additional feature such as rate control or admission control. If interference control is not used, the SA protocol suffers from the negatively infinite scaling exponent except the case of using rate control where a finite but suboptimal scaling exponent may be achieved. Also, it is shown that multi-hop control does not affect the scaling exponent but just improves the D-RATC pre-constant.

Performance analysis of a decode-and-forward based hybrid-ARQ protocol

Cooperative hybrid-ARQ protocols have been widely studied because the efficiency of time resources of them is higher than that of cooperative protocols. In this paper, a cooperative hybrid-ARQ protocol based on incremental redundancy hybrid-ARQ technique is proposed and analyzed with respect to the relay location. Based on the analysis, the optimum initial rate is searched and the maximum throughput is obtained with respect to the relay location.

The maximum achievable throughput of a decode-and-forward based hybrid-ARQ protocol

Cooperative hybrid-ARQ (HARQ) protocols have been widely studied because they are more efficient than cooperative protocols without HARQ. In [7], the throughput of a cooperative HARQ protocol based on the decode-and-forward protocol (DF-HARQ) is obtained. In this paper, the maximum achievable throughput of the DF-HARQ protocol is obtained using the asymptotic outage probability when the maximum number of transmission (M) goes to infinity. The range of the optimum worst-case coding rate (R) of the maximum achievable throughput is also obtained. Furthermore, we can expect that the methodology for obtaining the maximum achievable throughput in this paper also applicable to other cooperative HARQ protocols

Delay and Energy Constrained Random Access Transport Capacity

In this paper, we consider a delay and energy constrained wireless ad hoc network with node density of λ_n, where a packet should be delivered to the destination within D(λ_n) seconds using at most E(λ_n) energy in joules while satisfying the target outage probability. The performance metric for analyzing the network is the delay and energy constrained random access transport capacity (DE-RATC), i.e.,

Practical network-coding scheme for two-way relay channels employing a rate-compatible punctured code

C_ϵ(D(λ_n), E(λ_n), which quantifies the maximum end-to-end distance weighted rate per unit area of a delay and energy constrained network using a random access protocol. It is shown that a slotted ALOHA protocol is order-optimal under any delay and energy constraints if equipped with additional features such as power control, multi-hop control, interference control, and rate control, and the delay and energy constraints can be divided into three regions according to the relation between the physical quantities due to the constraints and those due to the node density and network size. The three regions are the non-constrained (NC) region, where the DE-RATC is given by Θ(√λ_n/logλ_n); the delay-constrained (DC) region, where the DE-RATC depends only on the delay constraint as Θ(D(λ_n); and the non-achievable (NA) region where a packet delivery under the given constraints is impossible. Also, it is shown that an arbitrary tradeoff between the rate of each source node and the number of source nodes can be achieved while keeping the optimal capacity scaling as long as λ_s=Ω√λ_n/logλ_n, Dλ_n))).

Joint feedback design for multiple access channel

A cooperative communication in a two-way relay channel is a bidirectional communication between two terminals with the aid of a common relay. In order to improve the performance of the cooperative communication in a two-way relay channel, a network coding can be used to exploit the broadcasting nature of wireless transmission. In [8], it was shown that each individual link can achieve its own capacity when the length of the codewords is the same. However, the length of the codewords can be different in practical systems since the two-way relay channel is naturally asymmetric. Thus, in this paper, we show a practical network coding scheme with a given modulation and coding set by employing a rate-compatible puncturing technique. Simulation results show that the proposed scheme can provide at least as good performance as that obtained in individual link without using special encoder/decoder.

Throughput analysis of MIMO cooperative decode-and-forward HARQ protocols

We study joint feedback design for multiple access channel (MAC) over fading Gaussian Channel. The transmitters use partial channel-state information (CSI), which is obtained via an optimized feedback link. We develop a simple iterative algorithm for the design of CSI quantization to maximize the expected rate. Also, we show the performance by simulation result.

Robust Space Time Code for Channel Coded MIMO Systems

We consider MIMO-HARQ protocols with/without relay under block fading channels with the assumption that the source, destination, and relay are half-duplex nodes with two antennas. The achievable rate of 2×2 MIMO-HARQ protocols are obtained when the number of retransmissions is unlimited and the optimum ratio between the two streams of two antennas is obtained. The MIMO-HARQ protocol without relay can achieve the ergodic capacity and the proposed MIMO-HARQ protocol with relay is a near capacity approaching scheme.

Efficient Adaptive Transmission Technique for Coded Multiuser OFDMA Systems

Various space time code (STC) designs have been proposed to obtain full diversity at full rate in multiple-input multiple-output (MIMO) channels for uncoded systems. However, commercial wireless systems typically employ powerful channel codes such as turbo codes and low density parity check (LDPC) codes together with an STC. For these applications, an STC optimized for uncoded systems may not provide the best performance. In this paper, an STC with relatively good performance over a wide range of code rates is proposed. Simulation results show that the performance of the proposed robust STC is very close to the best performance of the SM and the Golden code in various code rates.

Cooperative Hybrid-ARQ Protocols: Unified Frameworks for Protocol Analysis

In previous literature on adaptive transmission in multiuser OFDMA systems, only uncoded case or capacity (coded with infinite length of codeword) has been considered. In this paper, an adaptive transmission algorithm for coded OFDMA systems with practical codeword lengths is investigated. Also, in order to keep the feedback overhead within a practical range, a two-step partial CQI scheme is adopted, which has both better performance and reduced feedback overhead compared to conventional partial CQI schemes. By allowing a long codeword block across all allocated sub-bands with appropriate power and modulation order allocation rather than using short codeword blocks to each sub-band, high coding gain can be obtained, which leads to performance improvement.