Among the wireless personal area networks, much attention has been placed on the HomeRF system due to the simple hardware complexity. In this letter, we propose several techniques for the HomeRF system. First, a DC-offset compensation technique is considered for HomeRF system. In addition, a decision directed channel estimation technique is proposed. The proposed techniques require no additional training sequence and a little additional hardware. And finally, a turbo coding technique is considered as a improved coding scheme. It is shown that the performance of the proposed algorithm is significantly improved in comparison with the conventional HomeRF system.

This letter addresses the performance degradation due to carrier frequency offset in an orthogonal frequency and code division multiplexing (OFCDM) systems with multiple transmit antennas. For the performance evaluation, the average bit error rate (BER) expression is derived taking account of the effect of a carrier frequency offset. Derived results show that the BER performance of the space-time coded OFCDM system is less sensitive to a frequency offset, compared to the normal OFCDM system.

Nowadays, the batteryless sensor system is widely used for Internet of things (IoT) system. Especially, batteryless backscatter system has a great significance in that it permits us to communicate without power supply devices. However, conventional backscatter system requires high power reader and this can be a problem with the communication efficiency. Therefore, this letter proposes a new transmission scheme on the batteryless backscatter system in order to solve this problem. In the proposed scheme, the mobile devices which embed Wi-Fi chipset are used as a reader. The tag obtains Internet connectivity from the reader. Since the tag can not decode the general Wi-Fi packet, new algorithm of the scheme uses a specially designed packet. In this letter, the designing method for the decodable packet is proposed. Moreover, the scheme implements beamforming to improve the reliability. By concentrating the power to the designated direction, the robust communication can be achieved. The simulation results show that the proposed scheme offers reliable Internet connectivity without extra battery.

Dual-hop wireless transmission is a technique by which the channel from the source to the destination is divided into two shorter links using relays. By using this transmission, the communications reliability is improved whereas the throughput might go down since the dual-hop transmission is performed by two times. In this letter, we propose a scheme that uses hierarchical modulation at the source and adaptive modulation based on cyclic redundancy check (CRC) code at the relays. The proposed scheme is evaluated in terms of the bit error rate (BER) and throughput performances.

Among spatial diversity schemes, orthogonal space-time block code (OSTBC) and cyclic delay diversity (CDD) have been widely studied for the cooperative wireless relaying system. However, conventional OSTBC and CDD cannot cope with change in the number of relays owing to low throughput or error performance. In this letter, we propose the space-time cyclic delay diversity (STCDD) scheme which provides good error performance and full rate. Simulation results show that bit error rate (BER) performance of the proposed STCDD is superior to that of OSTBC and CDD when sufficient quality of source-relay channels are guaranteed.

Transmit diversity generally requires more than one antenna at the transmitter. However, many wireless devices are limited by size or hardware complexity. Cooperative diversity techniques were proposed to overcome this limitation. Cooperative communication has been widely investigated to improve the performance of wireless communication. Unfortunately, most existing cooperative schemes have the common fault of decreased transmission rate because the destination should receive the decodable compositions of symbols from the source and the relay. In this letter, we propose a new cooperative model that uses spatial phase coding (SPC) for orthogonal frequency division multiple access (OFDMA). This technique is free from the rate-loss and allows seamless cooperative communication while its diversity gain matches that of the conventional multiple antenna technique. The proposed technique is evaluated in terms of bit error rate (BER) and simulation results show that the proposed cooperative scheme approaches the performance of conventional multiple antenna system when the link between users is guaranteed.

The Long Term Evolution (LTE) of mobile communication standard was designed by the 3rd generation partnership project (3GPP) to serve the requirements. Nowadays, the combining of the orthogonal frequency division multiplexing (OFDM) and the multiple input multiple output (MIMO) is supported in LTE system. The MIMO-OFDM is considered to improve data rate and channel capacity without additional bandwidth. Because the receivers get all transmission signals from all transmitters at the same time, many detection schemes have been developed for accurate estimation and low complexity. Among the detection schemes, the QR decomposition with M algorithm (QRD-M) achieves optimal error performance with low complexity. Nevertheless, the conventional QRD-M has high complexity for implementation. To overcome the problem, this letter proposes the low complexity QRD-M detection scheme in MIMO-OFDM systems. The proposed scheme has two elements which decide layer value and the limited candidates. The two elements are defined by the number of transmit antennas and the cardinality of modulation set respectively. From simulation results, the proposed scheme has the same error performance with the conventional QRD-M and very lower complexity than the conventional QRD-M.

In this letter, a cooperative scheme is proposed for the broadcasting and cellular communication system. The proposed scheme improves bit error rate (BER) performance and throughput on the edge of a cellular base station (CBS) cooperating with another CBS in the same broadcasting coverage. The proposed scheme for the enhancement of BER performance employs two schemes by a channel quality information (CQI) between a broadcasting base station (BBS) and users. In a physical area, the edge of a CBS is concatenated with the edge of another CBS. When users are on the edge of a CBS, they transmit simultaneously the CQI to CBSs, and then a BBS and CBSs transmit signals by the proposed algorithm. The two schemes apply space-time cyclic delay diversity (CDD) and a combination of space-time block code (STBC) with vertical Bell Laboratories Layered Space-Time (V-BLAST) to a signal from a BBS and CBSs. The resulting performance indicates that the proposed scheme is effective for users on the edges of CBSs.

As dual-polarized multiple-input multiple-output (MIMO) technique has little inter-antenna interference, it provides high data rate and reliability to a user equipment (UE) with the low system complexity. In the joint transmission (JT) technique of the coordinated multi-point (CoMP) transmission system, multiple transmission points (TPs) transmit the same data to the UE so that the UE can get the diversity gain and the high reliability, especially at the cell-edge. However, the system performance of the dual-polarized MIMO in the JT technique of CoMP system is very sensitive on the dual-polarized channel state when the channel is asymmetric. In this letter, an improved dual-polarized MIMO scheme for JT of the downlink CoMP transmission system is proposed. This scheme adaptively applies the transmission power to each dual-polarized MIMO antenna and the modulation order of the transmission data according to the channel state information (CSI). System-level simulation results show that the proposed scheme provides better bit-error-rate (BER) performance in the asymmetric dual-polarized channel state than the conventional scheme.

In this letter, a robust algorithm for jointly finding an estimate of the start of the frame and transmission mode is proposed in a digital audio broadcasting (DAB) system. In doing so, the use of differential-correlation based joint detection is proposed, which considers not only the height of correlation peak but also its plateau. We show via simulations that the proposed detection algorithm is capable of robustly detecting the start of a frame and its mode against the variation of signal-to-noise ratio, providing a performance advantage over the conventional algorithm.

We design a DAB system using space-time coding for reliable transmission in the multipath fading channel. This letter assess the performance evaluation of space-time coded DAB system. For channel estimation in the space-time coded DAB system, we introduce two training sequences and derive the mean square error of each training sequence. We then represent the average symbol error rate of the space-time coded DAB system for the specific cases of two, three, four transmit antennas.

The multiple-input multiple-output (MIMO)-Orthogonal frequency division multiplexing (OFDM) system has a serious drawback in that it has high peak-to-average power ratio (PAPR). Therefore, in this letter, we propose an effective PAPR reduction scheme for MIMO-OFDM systems with nonlinear high power amplifier (HPA). The proposed scheme very effectively reduces the PAPR through the adaptive nonlinear estimator (ANE) which estimates the MSE between the OFDM signals before and after the nonlinear HPA and the low probability of false side information (SI) by receive diversity.

In this letter, we present a coarse frequency-offset synchronization technique for Eureka-147 DAB receiver. The proposed frequency-offset synchronization algorithm using two defined correlation functions is shown to have high robustness against a large range of symbol timing offset with a moderate implementational complexity.

The sub-channel is empty except each user's allocated sub-channel in an orthogonal frequency division multiple access (OFDMA) system. The scheme of cooperative communication using this empty sub-channel has been studied. But, because each user wastes the time slots in the cooperation phase, it is difficult to achieve the full rate. In this letter, a new cooperative communication scheme based on OFDMA is proposed to improve transmission rate in Rayleigh fading channel.

In this letter, we provide a performance evaluation of a Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) with adaptive modulation in a multipath fading channel. The MB-OFDM system in conjunction with adaptive modulation technique can be considered as one of the solutions for severely degraded channels such as those common in frequency selective fading environments.

In this letter, we propose an improved timing offset estimation scheme without making use of pilot symbols in the HomePlug Green PHY (HomePlug GP) standard. In contrast to the conventional decision-directed timing estimation scheme, the proposed scheme exploits the inherent repetition information of the HomePlug GP signals, thus not only removing the need for the estimated data or pilot symbols but also improving the timing estimation performance.

Combining a layered space-time receiver with the OFDM for high-rate transmissions requires the multi-channel estimation process. Therefore, this letter highlights a design of a preamble structure for OFDM-based layered space-time receiver. The new proposed preamble can estimate the multi-channel up to the 8 transmit antennas using two long preambles in the WLAN standards.

This letter proposes a modified orthogonal frequency division multiplexing (OFDM) signal with low peak-to-average power ratio (PAPR). As the case of previous works, OFDM system exploits a frequency diversity by using a simple symbol repetition. From the presented results, we can see that three modified OFDM signals using one transmit antenna can be implemented with low PAPR, still maintaining the same diversity gain at the receiver as in [9],[10].

Orthogonal frequency and code division multiplexing (OFCDM) is available as orthogonal frequency and code division multiple access (OFCDMA) by allocating subcarrier to users. OFCDMA is an efficient transmission method assigning the subcarrier and the channel code according to channel state or many different environments. However, OFCDMA is hard to apply many frequency spreading codes when it is compared with OFCDM because of the restrictive subcarriers. This problem leads to decrease the frequency diversity. Therefore we propose system that combines cyclic delay diversity (CDD) with cooperative relaying system based on OFCDMA. This system complements this restrict by spatial diversity. In addition to that, the proposed system obtains diversity gain without loss of the throughput when direct-path condition is not good.

The breadth-first tree searching (BFTS) detection algorithm such as the QR decomposition with M algorithm (QRD-M) which is the generally K-best detection algorithm is suboptimal, but has high complexity. In this letter, the K-best BFTS detection algorithm having reduced complexity is proposed. The proposed detection algorithm calculates the channel condition to decide the thresholds for regulating complexity and performance and from the simulation results, it has good error performance with very low complexity.