In this paper, we propose a 2-D RAKEreceiver architec- ture with fast Fourier transform (FFT)-based matched filtering.
Here, we consider an uplink CDMA system in which a pilot signal, which is associated with a data signal, is used for channelsounding. This 2-D RAKEreceiver is in reality a spatial–tem- poral 2-D matched filter. In order to reduce the computation complexity, all the signal processing are performed in the spa- tial–temporal frequency domain. Previous analysis and simula- tion results have shown that CDMA interference signals in the spatial domain can be considered to be spatial white Gaussian random variables, even when a small number of users with a moderate angle spread coexist in the system , . In this case, the optimum combining of antenna array signals can be
(22) A conventional RAKEreceiver first uses a sliding correlator to search for the multipath delay profile and a few tracking loops to acquire the channel parameters, such as the delays and the complex gains of the main paths. Then it uses multiple RAKE fingers to detect data. Unlike a conventional RAKEreceiver, both path searching and tracking are done implicitly in our channelsounding subsystem because it searches and tracks all paths within one symbol period in the time domain. In a cellular system, the multipath structure may change abruptly, for example, when a vehicle turns around a street corner. The sliding correlator of a conventional RAKEreceiver suffers from the estimation delay involved in searching for the multipath delay profile. Therefore, a conventional RAKEreceiver may lose track of some newly arrived or disappeared paths, and this will degrade the system performance. At contrast, our RAKEreceiver induces much less estimation delay since our path searching and tracking are done on a symbol-by-symbol basis and it can be quickly adapted to the change of the channel.
performance of the spread spectrum system requires the receiver’s phase and frequency and its chip timing to be perfectly synchronized. The synchronization process is called code acquisition. Acquisition is based on the received signal’s magnitude of the impulse response of the mobile channel and sets the delay times of the RAKE fingers. The typical RAKEreceiver architecture with maximal ratio combining is shown in Figure 1. The matched filter correlates the received signal with local PN code to obtain the delay profile of the multipath fading channel. The searcher is required to search the correlation profile. In the searcher, the threshold is set to select the peak values properly. It must set to obtain the acceptable missing probability false alarm probability.
2 In this paper, a space-time RAKE (ST-RAKE) with an interference-blocking (IB) scheme is proposed for combating the strong interference in CDMA communications systems. Specifically, a scheme is developed firstly to construct an IB transformation for removing the strong interference, while other signals retained. From the fact that the power level of the signal is well below that of the strong interference, the interference term can be approximately expressed in terms of the dominate eigenvectors corresponding to the larger eigenvalues of the received data correlation matrix.
In this paper, an adaptive ST RAKEreceiver is proposed for sectored CDMA systems .
In a sectored system, the entire field-of-view of the receiver is divided into several angular sectors, with each sector responsible for a distinctive set of users. With an antenna array in- corporated, sectorization can be done adaptively to meet the following two requirements. First, multiple beams are formed to collect desired signal multipath components in the designated angular sector. Second, strong MAI from outside the sector are suppressed in the sidelobe of these beams. These can be achieved by performing adaptive nulling on a set of beams steered to different look directions. To avoid signal cancellation incurred with coherent multipaths or mismatch of steering vectors in adaptive nulling, a modified GSC is employed to construct a set of linearly constrained minimum variance (LCMV) beamformers . The output of these beamformers are processed by a bank of adaptive correlators, which can be regarded as a set of LCMV combiners in the temporal domain. A modified GSC is again employed to collect the multipath components and suppress the in-sector MAI. The beamformers and correlators to- gether constitute a pre-despread beamspace-time (BT) processor, which performs the function of a RAKEreceiver. With MAI successfully suppressed, a simple maximum ratio combining (MRC) criterion can be used to determine the weights of the BT RAKEreceiver. Compared to the conventional ST receiver, beamspace sectored processing can potentially increase the sys- tem capacity by suppressing out-of-sector MAI, and also lower the computational complexity by reducing the spatial dimension. The proposed BT receiver is blind in that the construction of adaptive beamformers, correlators, and MRC is done without the aid of a training signal.
I. I NTRODUCTION
Multi-channel optical links suffer from less cross talk and EMI compared to their electrical counterparts, and are considered as promising technologies for data intensive platform and ultra high speed chip to chip interconnects. To take these advantages, low cost and small form factor optical transceivers incorporating silicon photo detectors are key components to enable pervasive adaptation. However, the intrinsic bandwidth of CMOS detectors in general is limited below hundreds of MHz. For over Gbps operations, they usually demand sophisticated equalization scheme . In order to circumvent the speed limitation of the detector, optical link incorporating pulse amplitude modulation (PAM) can improve its spectral efficiency so as to boost up the data bandwidth. In this scenario, an AGC loop is needed to replace conventional limiting amplifier in the receiver chain. On the other hand, the locking speed of the gain control loop is also of special interests to retain its channel efficiency .
dual-dimension Rakereceiver for the MC-DS-CDMA system. In order to validate the accuracy of the derivative, a lot of numerical results are conduct in this paper. It is worthwhile claiming that is not only the fading parameter of the correlated-fading model dominates the system performance of the MC-DS-CDMA system, but the number of antennas also definitely affects the system performance.
This research work was supported by the National Science Council of the Republic of China under grant number NSC 90-2219-E-002-011.
the subspace  methods. The subspace method, in particular, has also been applied to channel estimation for single-user OFDM systems [4-6]. A subspace-based approach is proposed in  to directly estimate the frequency-domain channel gains for single-user OFDM systems. In , a subspace-based channel identification algorithm is proposed for a single-user OFDM system without cyclic prefix. And in  it is proposed to use the autocorrelation of the vector that consists of all received signal samples to perform subspace-based blind channel estimation for single-user OFDM systems. While these approaches achieve good performance for the single-user case, some generalizations are necessary if they are to be applied to multi-user OFDM systems.
moreover, operating at undetermined environment, the systems face problems to estimate random parameters under different noise level and channel conditions, and need hundreds of packets to be tested for PER under one condition. All these factors mentioned previously make it very difficult to use only test patterns to verify the design. Besides, it is important to consider relation with analog and RF components. Therefore an integrated simulation platform shown in Fig. 11 is adopted to co-simulate baseband, analog and RF signals. For PER testing the transmit sequence is generated and coded with CRC-16, and then the MAC-to-TX interface serves to move the data from MAC to transmitter. After coding and modulation in transmitter, the data signal conforms to OFDM WLAN specification and outputs with 2x over-sample (40 MHz/sample) with 10-b resolution. The LPFs after DAC use 5th-order elliptic filter to remove duplicate spectra but result in nonlinear phase response and transmission ripples, which can
I. I NTRODUCTION
Terrestrial Digital Video Broadcasting (DVB-T) is a next-generation standard for wireless broadcast of MPEG-2 video . In order to provide the high data rate required for video transmission, concatenated-coded orthogonal frequency division multiplexing (OFDM) has been adopted into DVB-T. In order to cope with a multitude of propagation conditions encountered in the wireless broadcast channel, many parameters of OFDM for DVB-T can be dynamically changed according to channel conditions. In particular, the number of OFDM subcarriers can either be 2048 (2K) or 8196 (8K) so that the desired trade-off can be struck between inter-symbol interference (ISI) mitigation capability and robustness against Doppler-spread . As a result, a “mode detector” that detects the number of subcarriers in the transmitted OFDM symbol is required in a DVB-T receiver. Furthermore, time and frequency synchronization as well as channel estimation are also required as in any OFDM transmission system. Note that these operations can be performed and the transmitted information detected only after the correct number of subcarriers has been determined. Therefore mode detection must be done prior to synchronization and channel estimation in a DVB-T receiver. In principle, mode detection can be carried out by detecting the positions of pilot subsymbols. However, this method requires the knowledge of the pilot pattern and is therefore system-dependent. In this paper, a new algorithm is proposed for blind mode detection. The proposed algorithm exploits the cyclic nature of OFDM signals and difference in symbol durations to distinguish between different numbers of subcarriers. It will be shown in this paper that the proposed algorithm is simple and effective. Furthermore, since pilot subsymbols are not required, the proposed method is system-independent
personalized channel preload over IEEE 802.16e
Sheng-Tzong Cheng, Chih-Lun Chou, Gwo-Jiun Horng * and Tun-Yu Chang
The Internet protocol television (IPTV) is emerging as one of the most promising applications over next generation networks. The recently released IEEE 802.16d/e is capable of ensuring high bandwidths and low latency, making it suitable for delivering multimedia services. In addition, it also provides wide area coverage, mobility support, and non-line-of-sight operation. In this article, we deliver IPTV streaming over 802.16 wireless systems and propose a simple but effective IPTV channel-switching algorithm to keep the channel zapping time in a tolerable range. In addition, we discuss how to allocate channels in the limited bandwidth over wireless networks, such as 802.16. The proposed algorithm is based on hot-view channel and personal favorite channel preloading to reduce the network delay and achieve the goal of fastchannel switching. Finally, the experimental results show the performance of the proposed algorithm.
The performance metric of our problem is not a minimal the average access time but the percentage of information demands satisfied by the server.
2.2 System Architecture
Server Side: The broadcast server is divided into two modes, the broadcast mode and the on-demand mode. Each data item in the database is classified as belonging to one of these two modes, denoted as a broadcast data set and an on-demand data set, respec- tively. Moreover, the bandwidth for broadcast is divided into m + 1 channels. One of the channels is reserved for the delivery of broadcast schema. The broadcast schema con- tains information about the broadcast data set. The broadcast scheduler generates a peri- odic broadcast program on the m broadcast channels. Because the clients are equipped with multiple receivers, the pages of a data item can appear in more than one channel at the same time. By using the bandwidth remaining for the on-demand mode, the on-demand scheduler selects a request to be served and broadcasts the requested data items in an online fashion.
adaptive filter bank, copied from the lower branch, performs despreading and MAI suppression, and pilot symbols assisted frequency offset estimation, channel vector estimation and RAKE combining give the desired signal symbols. With signal subtraction in the lower branch, the proposed MC-CDMA re- ceiver can achieve nearly the performance of the ideal MSINR receiver within a few iterations. Finally, a low-complexity PA realization of the GSC adaptive filters is presented for a multiuser scenario. The new PA receiver is shown to be robust to multiuser channel errors, and offer nearly the same perfor- mance of the fully adaptive receiver. In summary, the proposed MC-CDMA receiver with PA MAI suppression performs near optimal signal detection with tolerance to large frequency offsets and resistance to strong MAI. More importantly, it can be initialized in the blind mode without the aid of channel estimation and frequency offset compensation.
This project is to research the performance and receiver design of GMSK modulation system for mobile communication. In this channel, because of the affection of environment, the signals would be distorted. We consider the fading noise and additive Gaussian white noise in the project. In receiver, through our analysis, we suggest to use linear prediction technique to treat the data before,and match Viterbi algorithm to demodulate them. This project is to research and analyze GMSK structure and design adaptiveoptimum receiver system characteristic, and compare to the characteristic ofcomputer simulation, and combine theory and simulation.