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Code division multiplexing (CDM)-based random access, wherein a set of sequences is reserved for random access and a remote station transmits a random access packet using a sequence randomly selected from this set, is employed in numerous practical wireless systems. If multiple remote stations simultaneously transmit random access packets using the same sequence, the performance degrades owing to sequence collision. In addition, the performance is degraded because of interference if multiple remote stations simultaneously transmit random access packets using different sequences. Therefore, the performance of CDM-based random access is dependent on both sequence collision and interference. There have been no previous studies on analyzing the performance of CDM-based random access considering both sequence collision and interference. In this paper, the throughput of CDM-based random access is investigated considering both sequence collision and interference based on a signal-to-interference-plus-noise ratio (SINR) capture model. Analyses and numerical simulations are performed to compare the throughputs of several random access schemes, including conventional and channel-adaptive random access. The results show that channel-adaptive random access can achieve significantly higher throughput than that achieved by conventional random access. Moreover, the results demonstrate that it is possible to analyze the trade-off between the throughput and implementation complexity with the increased the number of sequences. [ABSTRACT FROM AUTHOR]

In this paper, performance is investigated for a random access packet composed of a preamble and message. To minimize the error probability of a packet with channel-adaptive random access, the optimum energy allocation is obtained between the preamble and the message. The performances with the optimum and sub-optimum energy allocations are compared by simulation. [ABSTRACT FROM AUTHOR]

Channel-adaptive random access is proposed to reduce the required transmission power for random access in TDD-based wireless systems. With channel-adaptive random access, a remote station measures the channel state of the downlink, estimates the channel state of the corresponding uplink based on the downlink measurement, and transmits a random access packet only when the channel satisfies a predetermined transmission condition. Thus, transmission is delayed until the channel satisfies the transmission condition. With conventional channel-adaptive random access, a remote station continuously measures the channel state to check if the channel satisfies the transmission condition, which consumes a large amount of power. In this paper, we propose a discontinuous channel measurement scheme for channel-adaptive random access to reduce the power consumption. The performance of the proposed method is investigated in terms of the detection performance of a random access packet, transmission delay, and the power consumption of the receiver. [ABSTRACT FROM AUTHOR]

Channel-adaptive random access can reduce the power required for successful random access transmission in a TDD-based wireless system. With channel-adaptive random access, transmission of a random access packet is delayed until a predefined channel condition is satisfied. The performance of channel-adaptive random access has been investigated with suboptimal power allocations including constant and channel inversion power allocations. However, the optimal power allocation has not been studied for channel-adaptive random access. In this paper, the optimum power allocation is derived for channel-adaptive random access, especially considering the detection performance of a random access preamble. Some important properties are investigated for the optimum power allocation. Numerical results compare the performances of the optimum and the suboptimal power allocations. [ABSTRACT FROM PUBLISHER]

In this paper, a channel-adaptive random access transmission scheme is presented for time-division-duplex (TDD)-based wireless systems. In a TDD-based wireless system, using the channel reciprocity, the channel gain of an uplink (UL) can be estimated from that of a downlink. The channel-adaptive random access scheme allows the transmission of a random access packet only when the channel gain of the UL is higher than a predetermined threshold. With channel-adaptive random access, it is possible to reduce the power required for random access transmission drastically at the cost of slightly larger transmission delay. If the threshold is set to zero, the presented channel-adaptive scheme is exactly the same as the conventional random access scheme. Therefore, channel-adaptive random access provides system design flexibility with the tradeoff between transmission power and transmission delay. [ABSTRACT FROM PUBLISHER]

In this letter, for general fading distributions, it is rigorously shown that the water-filling power allocation function converges pointwise to the function which allocates fixed power to all non-zero channel gain states, as SNR approaches infinity. The convergence speed of the water-filling power allocation is also investigated. [ABSTRACT FROM PUBLISHER]