In this paper we study propagation properties of multi-user MIMO systems in narrow indoor corridor environments. From extensive channel measurements, it is observed that the channels to different ...users often experience very high or very low orthogonality. As a consequence, the gain of optimal dirty-paper-coding, or any other coding scheme, over linear processing techniques becomes insignificant.
Fast and reliable time and frequency synchronization is crucial for packet-based orthogonal frequency division multiplex (OFDM) systems. In this paper we compare and analyze preambles for OFDM ...systems based on repeated OFDM data symbols or repeated short pseudonoise sequences (PN-sequences). We make an analytical evaluation for AWGN channels and simulate the performance in oneand two-tap Rayleigh fading channels. The PN-based preamble gives better detection properties in terms of lower false detection probability and lower probability of missing the synchronization signal. The PN-based preamble has low peak-to-average power ratio and it makes it possible to use an ADC with one-bit quantization in stand-by mode. For frequency offset estimation both preambles give similar performance, but the PN-based preamble allows for a greater reduction in stand-by mode power consumption.
In this paper, we present an analysis of different channel estimator structures that can be used and efficiently implemented with minor configuration changes of a common hardware for both LTE and ...DVB-H. Such common estimator structures for LTE and DVB-H allow algorithm and hardware reuse when both standards are implemented on the same platform. In this approach, a core estimator will be utilized to address parameter estimation for the two standards. The estimators exploit similarities in pilot patterns between LTE and DVB-H. The estimation techniques are discussed taking both algorithm and complexity issues into account.
In sensor network applications, the use of duty-cycled ultra-low power wake-up receivers can significantly reduce overall power consumption. An important complement to previous investigations is to ...show that low-power wake-up receivers with good enough detection performance can be realized in hardware. In this paper we address this very issue by presenting the design, implementation, and sub-VT characterization of a digital back-end for such an ultra-low power WRx.
This paper presents a low-complexity energy efficient channel pre-processing update scheme, targeting the emerging 3GPP long term evolution advanced (LTE-A) downlink. Upon channel matrix renewals, ...the number of explicit QR decompositions (QRD) and channel matrix inversions are reduced since only the upper triangular matrices R and R -1 are updated, based on an on-line update decision mechanism. The proposed channel pre-processing updater has been designed as a dedicated unit in a 65 nm CMOS technology, resulting in a core area of 0.242mm 2 (equivalent gate count of 116K). Running at a 330MHz clock, each QRD or R -1 update consumes 4 or 2 times less energy compared to one exact state-of-the-art QRD in open literature.
This paper presents a novel memory optimization technique to exploit the analogy between correlation coefficients in MMSE-based channel estimators across multiple standards. The need for coefficient ...storage for robust MMSE channel estimators is expensive in terms of on-chip memory. Besides, the memory requirements grow linearly by integrating more standards onto one platform. Thus, it becomes inevitable to address the increased on-chip memory problem for such estimators. In this paper, we have shown that by exploiting the inherent similarities between LTE and DVB-H design parameters, a three-fold memory optimization may be achieved with minimal performance loss.
We present a pipelined implementation of an iterative threshold detector, which makes the same decisions as a maximum likelihood sequence detector (MLSD) on some, but not necessarily all, bits. We ...apply this as a first stage detector in a direct sequence code division multiple access (DS-CDMA) interference-limited multiuser system. In combination with the single-user matched filter (MF) detector we obtain improved performance and lower complexity than with the decorrelating receiver for a limited number of simultaneous users, e.g. up to 25 users with a spreading factor of 127.
In this paper two simplified transform based estimators for MIMO OFDM systems using the DFT and an SVD based transform are compared over a tapped delay line channel model. In the resulting symbol ...error rate plots, it is seen that the DFT based estimator experiences an error floor caused by the mismatch between the discrete time model and a continuous time reality. This error floor becomes a problem at high SNR levels where high data-rate systems can be expected to operate. When using an SVD based estimator it is seen that this error floor is reduced at the cost of a somewhat increased estimator complexity
This paper describes two interleaver structures that reduce the memory requirement for the storage of interleaver rules. The first structure offers memory reductions of more than 50%, compared to ...storing the entire interleaver vector. The second structure is useful when a range of interleaver sizes are to be stored, offering memory reductions asymptotically approaching 50%. By combining the two structures, a total memory reduction of approximately 75% is achieved. This is obtained without any significant reduction of the error correcting performance of the codes.
It is essential to find suitable modes (combinations of alphabet sizes and code rates) for transmission in cellular systems. Bad choices result in low spectrum efficiency. An analytical method is ...proposed to find the modes which give the highest spectrum efficiency when using adaptive modulation. It is demonstrated that data rates considerably higher than 271 and 384 kbps are feasible in GSM and EDGE systems by using adaptive modulation. It is further demonstrated that the spectrum efficiency can be improved more than 100% by using three modes in a GSM system.
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