Hybrid automatic repeat request (HARQ) is employed for the Evolved Universal Terrestrial Radio Access (E-UTRA) downlink. The base station not only decodes the ACK/NACK signals from the user equipment (UE), but also detects a termination of the transmission (DTX) of the ACK/NACK signals caused by the mis-detection of the downlink control information (DCI) at the UE side. Since ACK/NACK signals from UEs are multiplexed by CDMA, there are sometimes severe inter-code interference (ICI) effects, which significantly degrade the performance of ACK/NACK signals. In order to mitigate such ICI effects, in [1],[2], we proposed a novel phase rotation scheme on the constellations of the uplink ACK/NACK signals, and confirmed the effects on the ACK/NACK bit error rate performance; however, the previous paper did not analyze the effects of the phase rotation on the DTX detection performance. Hence, in this paper, we further analyze the effects of the phase rotation for the ACK/NACK signals in conjunction with a new DTX detection scheme which utilizes equalizer outputs, and investigate the performance of the proposed scheme by means of computer simulations.

Advanced Evolved Universal Terrestrial Radio Access (Advanced E-UTRA), called LTE-Advanced, has been standardized in the 3rd Generation Partnership Project (3GPP) as a candidate for IMT-Advanced. LTE-Advanced supports spatial orthogonal-resource transmit diversity (SORTD) [1],[2] for ACK/NACK signals and scheduling requests (SRs), which are used to control downlink hybrid automatic repeat requests (HARQs) and manage uplink radio resources based on uplink data traffic, respectively. Both ACK/NACK signals and SRs are carried via a physical uplink control channel (PUCCH) [3], and a common PUCCH format is used for both ACK/NACK signals and SRs. If SORTD is used, the base station assigns mutually orthogonal resources to each antenna included in the user equipment (UE) for ACK/NACK signals and SRs; hence, the number of required resources increases with the number of transmitting antennas in the UE. In this paper, we study the resource reduction method for ACK/NACK signal and SR in case of SORTD using the concept of common resource. In addition, we investigate a phase rotation scheme for common resources to improve the SR detection performance.

Hybrid automatic repeat request (HARQ) is employed for the Evolved Universal Terrestrial Radio Access (E-UTRA) downlink. Each user equipment (UE) sends its ACK/NACK corresponding to the downlink data reception to the base station via a physical uplink control channel (PUCCH). The ACK/NACK signals from the UE are first code spread by the cyclic shift (CS) sequences, and then code spread again by the orthogonal cover (OC) sequences. The ACK/NACK signals from each UE are multiplexed by means of code division multiple access (CDMA), however, it is difficult for the conventional PUCCH code design to satisfy the required bit error rate (BER) of 10-3 [1] in fast-fading environments because of inter-code interference (ICI) among the OC sequences. Therefore, resource management of PUCCH is required depending on the mobility of the UEs to maximize the performance of the ACK/NACK signals and the capacity of PUCCH simultaneously. In this paper, we propose a novel code design for PUCCH, which can suppress the effects of ICI among the OC sequences, and thus can simplify the resource management of PUCCH. The simulation evaluations confirm that the proposed code design can significantly improve the performance of the ACK/NACK signals via PUCCH in fast-fading environments, and any complicated resource management based on the mobility of the UEs are not necessary.

Hybrid automatic repeat request (HARQ) is employed for the Evolved Universal Terrestrial Radio Access (E-UTRA) downlink. The ACK/NACK signals from each user equipment (UE) are multiplexed by code division multiple access (CDMA) and transmitted via a physical uplink control channel (PUCCH). The ACK/NACK signals are code spread by the cyclic shift (CS) sequences made from zero auto-correlation (ZAC) sequences; however, the orthogonality of these sequences is not guaranteed depending on the propagation channels; moreover, the amount of inter-code interference (ICI) depends on the delay spread of the channel and the transmitting timing control error of each UE. In the conventional PUCCH structure, ICI between two ACK signals does not degrade their detection performance, whereas ICI between an ACK signal and a NACK signal degrades the detection performance. This causes a serious gap between the detection performances of ACK and NACK signals, because generally in a PUCCH, there are more ACK signals than NACK signals. In this paper, we propose a novel phase rotation scheme on the constellations of ACK/NACK signals that can resolve this issue, and the simulation evaluation results confirm the benefits of the proposed phase rotation scheme.

We propose an inter-cell interference coordination (ICIC) method that employs inter-cell coordinated transmission power control (TPC) based on inter-cell interference power in addition to conventional received signal power-based TPC in the cellular uplink. We assume orthogonal multiple-access as is used in 3GPP LTE. In the proposed method, an ICIC effect similar to that for conventional fractional frequency reuse (FFR) is obtained. This is achieved by coordinating the allowable inter-cell interference power level at the appropriate frequency blocks within the system bandwidth among neighboring cells in a semi-static manner. Different from conventional FFR, since all users within a cell can access all the frequency blocks, the reduction in multiuser diversity gain is abated. Computer simulation results show that the proposed method enhances both the cell-edge and average user throughput simultaneously compared to conventional universal frequency reuse (UFR) and FFR.

Research in smart antenna technology has progressed over the past few years and is gradually reaching the phase of practical use. We have developed a smart antenna test bed for wireless local area network (LAN) that is based on the IEEE802.11b. The objective is to improve anti-multipath fading performance and expand communication distance. Using this test bed, we carried out field tests in two environment. One environment is an office in an non line of sight (NLOS), and another environment is an outdoor in a line of sight (LOS). In this paper, we explain the outline of the test bed, the measurement method, and present the results of the field tests. In the office environment, we measured the performance of each set with a different number of antenna elements. The results show that the dead-spots where communication becomes impossible disappear if the number of antenna elements is more than or equal to two. In addition, a greater number of elements indicates better performance. The total average throughput is 1.6 times as efficient when two elements are used, and 1.9 times when four elements are used. Cold spots where the throughput is slower than 1 Mbps are reduced by 80-90%. In the outdoor LOS environment field test, it is shown that by using four-element smart antenna for both transmitter and receiver, the communication distance reached 1km with an average throughput of 4 Mbps. These results prove that the smart antenna drastically improves the performance of a wireless LAN system, i.e. the IEEE802.11b.

Many carriers are introducing multi-media services to satisfy customer demands for these services. In order to provide such services, carrier must increase their system capacity. It is well known that space division multiple access (SDMA) improves system capacity and is compatible with existing access systems. In order to evaluate the performance of SDMA, we developed an SDMA test bed. The test bed maintains the personal handy phone systems (PHS). The PHS adopts time division multiple access (TDMA). Aiming to compare the performance of SDMA and TDMA using the same analog hardware, the SDMA test bed employs a software-defined radio (SDR) technique. This paper shows the outline and performance of the test bed. The results of laboratory tests indicate that the bit error rate (BER) of the test bed operated in the SDMA mode at under 10-3 when the carrier-tointerference ratio (CIR) was larger than approximately -22 dB. Antenna patterns measured in an anechoic chamber show that the SDMA test bed produces correct antenna patterns when there are three desired signals and one interference signal. The results of the four field tests confirm that the test bed operated while two-multiplex SDMA mode doubled of the traffic and decreased the interference level as compared with the TDMA mode. Furthermore, the test bed operated while threemultiplex SDMA mode improves the traffic about 2.4 to 2.7 times. The SDMA test bed decreased the impact of the adjusted TDMA base station (BS). Therefore, we confirmed that the SDMA improves system capacity without any degradation.