We consider a hybrid direct-sequence frequency-hopped (DS/FH) code division multiple access (CDMA) communication system, where the transmission power, data rate (i.e. spreading gain), and hopping frequency are adapted relative to the channel variations. Instead of random frequency hopping, hopping pattern is adaptively adjusted to obtain the maximum channel gain among available frequency slots. Transmission power and/or data rate are also adapted such that a target transmission quality is maintained. It is shown that the proposed scheme provides a higher average data rate than pure DS/CDMA with power and rate adaptations, subject to the identical bandwidth and average transmission power constraints.

We propose a new broadcast strategy for a multiple-input multiple-output (MIMO) system with N transmit antennas at the transmitter and M≤N single antenna receivers. The proposed method, based on dirty-paper coding (DPC), spatially separates the M users but does not suffer from the power loss of classical spatial division multiple access (SDMA). For the special case of M=N=2 and when the two single antenna receivers are assumed to be co-located, the proposed scheme produces a 2 transmit, 2 receiver antenna MIMO transmission system that doubles the symbol rate of MIMO space-time block code (STBC) systems from one to two symbol per transmission time. It is proved theoretically and experimentally that the proposed scheme provides the same performance level as that of MIMO STBC systems (i.e., the Alamouti scheme) for the first symbol, and the same performance as the Bell labs layered space-time (BLAST) system for the second symbol. When compared to the BLAST system, the proposed scheme has the same symbol rate, but achieves significantly better performance, since it provides 2 level diversity per symbol on the first symbol while the BLAST system does not provide any diversity.

In this letter, we propose an Adaptive Modulation and Coding (AMC) scheme with relay protocols, such as Amplify-and-Forward (AF), Decode-and-Forward (DF) and De-Modulate-and-Forward (DMF). We perform simulations based on 3GPP Long Term Evolution-Advanced (LTE-A) parameters to compare the performance of an adaptive Modulation and Coding Scheme (MCS) using relay protocols of AF, DF, and DMF with non-adaptive MCS, with the same relay protocols. We analyze the performance of the proposed scheme and observe how the proposed AMC scheme with DMF performs at various Signal to Noise Ratio (SNR) regions. The simulation results have shown that the performance of the proposed AMC scheme with relay protocols of DMF is much better at lower and a higher SNR regions and also provides higher average throughput.

In this paper, we propose a system that adopts the independent MCS (modulation and coding scheme) level for each layer in the AMC (adaptive modulation and coding) scheme combined with the V-BLAST (vertical Bell lab layered space time) system. From the simulation results, we observe that since the independent MCS level case adapts modulation and coding rate for maximum throughput to each channel condition in separate layers, the combined AMC-V-BLAST system with the independent MCS level selection results in improved throughput compared to the combined AMC-V-BLAST system with the common MCS level selection and the conventional AMC system based on the 1x EV-DO standard. Especially, the combined AMC-V-BLAST system with the independent MCS level achieves a gain of 700 kbps in 7-9 dB SNR (signal-to-noise ratio) range.

This paper proposes a stabilized multichannel random access protocol based on slotted ALOHA for relay deployed cellular networks. To ensure the stability of random access, the proposed protocol dynamically controls the number of random access channels in a BS and a RS and the retransmission probability of the random access packets under heavy load conditions. A mathematical formula is also developed that derives an optimal partition ratio of the shared random access channels between a base station and a relay station without and with capture effect. Numerical results show that the proposed protocol can guarantee the required utilization and delay even in high offered load, which otherwise can cause bistable problem of slotted ALOHA.

We design a unified multicarrier (UMC) system for wideband communication. The proposed scheme can provide an effective and unified method that can implement a wideband CDMA system with high spectrum efficiency and flexibility because of the free selection of system parameters and a double spreading in the time and frequency domains. Also, separation of the spectrums carrying the same data to further ensure the independent fading between subcarriers is performed, that is, subcarriers are interleaved in the frequency domain. This frequency interleaving mitigates the effect of ISI and ICI. We also theoretically analyze the performance of the UMC system by deriving the closed-form solution for probability of bit error in a frequency selective Rayleigh fading channel. The analysis has proved that the UMC system has outperformed the conventional single carrier CDMA system under given conditions.

In this paper, in order to increase system capacity and reduce the transmitting power of the user's equipment, we propose a modified power control scheme consisting of a modified closed-loop power control (CLPC) and open-loop power control (OLPC). The modified CLPC algorithm, combining delay compensation algorithms and pilot diversity, is mainly applied to the ancillary terrestrial component (ATC) link in urban areas, because it is more suitable to the short round-trip delay (RTD). In the case of rural areas, where ATCs are not deployed or where a signal is not received from ATCs, transmit power monitoring equipment and OLPC algorithms using efficient pilot diversity are combined and applied to the link between the user's equipment and the satellite. Two power control algorithms are applied equally to the boundary areas where two kinds of signals are received in order to ensure coverage continuity. Simulation results show that the modified power control scheme has good performance compared to conventional power control schemes in a geostationary earth orbit (GEO) satellite system utilizing ATCs.

This letter contains our proposal for a new iterative decoding algorithm for Turbo coded V-BLAST system. The proposed algorithm is based on maximum a posteriori (MAP) decision criterion. In a V-BLAST system concatenated with Turbo codes, the extrinsic information from the soft output channel decoder can be utilized as a priori probability, making it possible to apply MAP decision criteria to the V-BLAST decoding process. The MAP decision criterion is applied to the V-BLAST ordering and slicing procedure, resulting in a considerable gain in bit error performance. As the iteration rate increases, the proposed system exhibits performance similar to that of system with ideal sliced.

In recent years, techniques such as multiple input multiple output (MIMO) and orthogonal frequency division multiplexing (OFDM) have been developed and combined in MIMO-OFDM systems to provide higher data rates. In addition, the system can be optimized by setting modulation and coding adaptively according to the channel conditions. The overall system performance depends on how accurately the system obtains the channel state information (CSI) and feeds it back to the transmitter. In this paper, we propose a signal-to-noise-ratio (SNR) estimation algorithm in which the preamble is known by both sides of the transceiver. Through simulations of several channel environments, we prove that our proposed algorithm is more accurate than traditional algorithms.

In this paper, we propose and analyze the adaptive modulation system with optimal Turbo Coded V-BLAST (Vertical-Bell-lab Layered Space-Time) technique that adopts extrinsic information from a MAP (Maximum A Posteriori) decoder with iterative decoding as a priori probability in two decoding procedures of V-BLAST scheme; the ordering and the slicing. Also, we consider the AMC (Adaptive Modulation and Coding) using the conventional Turbo Coded V-BLAST technique that simply combines the V-BLAST scheme with the turbo coding scheme. And we compare the proposed iterative decoding algorithm to a conventional V-BLAST decoding algorithm and a ML (Maximum Likelihood) decoding algorithm. In this analysis, the MIMO (Multiple Input Multiple Output) and the STD (Selection Transmit Diversity) schemes are assumed to be parts of the system for performance improvement. Results indicate that the proposed systems achieve better throughput performance than the conventional systems over the whole SNR (Signal to Noise Ratio) range. In terms of transmission rate performance, the suggested system is close in proximity to the conventional system using the ML decoding algorithm. In addition, the simulation result shows that the maximum throughput improvement in each MIMO scheme is respectively about 350 kbps, 460 kbps, and 740 kbps. It is suggested that the effect of the proposed iterative decoding algorithm accordingly gets higher as the number of system antenna increases.