Ye Hoon Lee

Effect of channel estimation errors and feedback delay on the performance of closed-loop transmit diversity system

We analyze the performance of closed-loop transmit diversity systems in the presence of feedback delay and channel estimation error in Rayleigh time-selective flat fading. We formulate both the feedback delay and the channel estimation error as a function of Doppler spread, and derive the average bit error probability under such imperfect channel information. It is shown that the channel estimation error is more sensitive to system performance than feedback delay in slow fading environments.

Wireless Ad-hoc Networks Using Cooperative Diversity-based Routing in Fading Channel

We propose new routing scheme, Cooperative Diversity-based Routing (CDR) which utilize the cooperative space diversity for power saving and for performance enhancement of wireless ad-hoc networks. The end-to-end performance of the proposed routing, CDR, is analyzed based on the Haenggis link model. The improved performance is compared with Multi-hop Relay Routing (MRR) by analytical methods. When the required outage probability is 1times10-3 at the destination node in ad-hoc networks with 7 nodes, we noticed that each node can save power consumption by 21.5 dB in average, by using our proposed CDR compared to MRR.

Double Opportunistic Transmit Cooperative Relaying System with GSC in Rayleigh Fading Channels

In a conventional opportunistic transmit (COT) cooperative relaying system, only the relays that receive signal-to-noise ratio (SNR) from the source and that exceed the threshold transmit to the destination. The COT system, however, only considers the SNR of the source-relay (S-R) path regardless that the SNR of the relay-destination (R-D) path is the opportunistic transmission condition. For that reason, it is not guaranteed that all the transmitted signals from relays exceed the threshold at the destination. Therefore we propose a double opportunistic transmit (DOT) cooperative relaying system - when both of the received SNR from a source and from a destination exceed the threshold, the relay transmits to the destination. It is shown that the proposed DOT system reduces power consumption by 6.9, 20.9, 32.4, and 41.4 % for K =3, 5, 7, and 9, respectively under the given condition of P out =1×10 ?3 and γ SR /Г SR =30 ㏈, compared to the COT system. We noticed that the performance of the DOT system is superior to that of the COT system for the identical number of active transmit relays under the same condition of the normalized average SNR of γ RD /Г RD .

Iterative Noncoherent Receiver for Differential STBC in Fast Fading Channels

An iterative noncoherent receiver that does not exploit channel statistics is proposed for the detection of differential space-time block codes (DSTBCs) in fast-fading channels. For robustness to channel variation, it employs an iterative architecture incorporating a priori information from a channel decoder in the Viterbi detection. Computer simulation shows that the performance of this iterative scheme is comparable with that of ideal coherent detection as the number of iterations increases.

Performance of closed-loop transmit antenna diversity system with channel estimation errors and fading correlation

The effect of channel estimation errors and fading channel correlation on closed-loop transmit diversity (CTD) systems is investigated in frequency flat Rayleigh fading channels. A bit error rate expression for the CTD system is analytically derived as a function of the channel correlation coefficient, feedback delay, and fading index. Numerical results show that the performance degradation caused by the estimation errors is more severe than that caused by the fading correlation. It is interpreted that the performance of the CTD system is more sensitive to the beamforming error rather than to the fading correlation.

Transmit power minimization for Poisson distributed wireless ad-hoc relay networks in Rayleigh fading channels

In this paper, power minimization for Poisson distributed random relay networks in Rayleigh fading channels is considered. We investigate two power allocation methods; one is a minimum power allocation (MPA) strategy and the other is an equal outage power allocation (EOPA) strategy. We analyze the total transmit power of two allocation methods under the given end-to-end outage probability constraint. Our results show that the MPA achieves more power saving than EOPA, and the power saving is more significant as the number of relay nodes increases.

Combined power and rate adaptions in DS/CDMA Communications over fading channels

We propose a combined power and rate adaptation scheme in direct-sequence code division multiple access (DS/CDMA) communications over Nakagami fading channels. The transmission power proportional to Gi p is allocated to the data transmission of user i, where Gi is the channel gain for user i, and p is a real number, and the data rate (i.e. spreading gain) is jointly adapted so that a desired transmission quality is maintained. We analyze the average data rate of the proposed adaptation scheme subject to fixed average and peak transmission power constraints. Our results show that the proposed joint adaptation scheme has considerable performance improvements over power only adaptation and rate only adaptation for a range of system parameters.

Optimal closed-loop transmit antenna diversity with average and peak power constraints

In a closed-loop transmit-antenna-diversity system, a closed-form expression for the optimal transmitter weights that minimize the average bit error rate (BER) is derived with fixed average and peak transmit power constraints. It is shown that the peak-power limitation degrades the average BER performance more significantly as the available average power and/or the number of transmit antennas increase.

Adaptive Adjustment of Integration Time for BPSK Based Ultra-Wideband Frequency Hopping Receiver

The frequency hopping (FH) based ultra-wideband (UWB) communication system divides its available frequency spectrum into several sub-bands, which leads to inherent disparities between carrier frequencies of each sub-band. Since the propagation loss is proportional to the square of the transmission frequency, the propagation loss on the sub-band having the highest carrier frequency is much larger than that on the sub-band having the lowest carrier frequency, resulting in disparities between received signal powers on each sub-band, which in turn leads to a bit error rate (BER) degradation in the FH UWB system. In this paper we propose an adaptive receiver for FH based UWB communications, where the integration time is adaptively adjusted relative to the hopping carrier frequency, which reduces the disparity between the received signal energies on each sub-band. Such compensation for lower received powers on sub-bands having higher carrier frequency leads to an improvement on the total average BER of the entire FH UWB communication system. We analyze the performance of the proposed reception scheme in Nakagami fading channels, and it is shown that the performance gain provided by the proposed receiver is more significant as the Nakagami fading index m increases (i.e., better channel conditions).

An Optimal Closed-Loop Transmit Antenna Diversity With Average and Peak Power Constraints

In a closed-loop transmit antenna diversity system, a closed- form expression for the optimal transmitter weights that minimize the average bit error rate (BER) is derived with fixed average and peak transmit power constraints. It is shown that the peak power limitation degrades the average BER performance more significantly as the available average power and/or the number of transmit antennas increase.