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Combining analog with digital beamforming in the sense of hybrid beamforming is one of the promising solutions to maximize throughput for millimeter wave links. Due to a concern of complexity, codebooks used in the analog beamforming are limited to their size. This paper shows that if the limited codebooks are made up of orthogonal steering vectors, the analog beamforming can be implemented with low...
In this paper, we study the joint impact of three major RF im-pairments, namely, oscillator phase noise, power amplifier non-linearity and I/Q imbalance on the performance of a mm-wave communication link based on OFDM modulation. General im-pairment models are first derived for describing the joint effects in each TX, each RX as well as a mm-wave communication link. Based on the obtained signal models...
Spatial channel estimation (CE) for hybrid beamforming architecture is one of the crucial challenges for millimeter wave (mmW) links. The limited beamwidth makes the CE incapable of resolving multiple channel paths from the same cluster when the angular spread is less than or equal to the beamwidth. Therefore, how to efficiently obtain reliable links which provide maximum spatial degree-of-freedom...
Efficiently estimating spatial channel properties, such as angles of arrival and departure, for a hybrid beamforming (HBF) architecture is one of the crucial challenges to overcome at millimeter wave (mmW) systems. To this end, we propose an algorithm variant to a recently proposed approach [8] based on ideas borrowed from the compressed sensing literature and /0-norm minimization, which exploit the...
In this paper, we propose an analog beamsteering approach for enabling flexible hybrid beamforming design that can achieve performance close to singular value decomposition (SVD) based digital beamforming with single user case. As a starting point, assuming the use of a codebook with infinite precision, we apply transposes of antenna array response matrices as analog beamformers at the BS and the...
In this work we show that the analog equalizing networks are suitable for low resolution quantization with limited mutual information loss in strong line-of-sight MIMO communication. More specifically, a simplified analog equalizing network design in comparison with state-of-the-art works is proposed in this work. Additionally, the new network design works equally good for larger displacement ranges...
In this work, we show a new design of analog equalizing network for N-stream strong Line-of-Sight MIMO communication, aiming at improved robustness. The design includes a core fixed equalizing network that equalizes ideal spatially orthogonal channels. Existing works show that the fixed equalizing network can equalize a spatially orthogonal MIMO system with parallel arrays. However, it is observed...
Spread Spectrum CDMA systems suffer from interference in frequency-selective channels. For the uplink, Multiuser Detection (MUD) mitigates the interference. For the downlink, Multiuser Transmission (MUT) is possible, provided that an estimation of the channel impulse response is available. A novel MUT approach is proposed, which outperforms other MUT methods, like Joint Transmission (JT) and die Transmit...
Oscillator phase noise present in OFDM systems limits the performance by producing a common phase error and additional intercarrier interference. While phase noise is most often modelled as a Wiener process corresponding to free running oscillators, we use a recently developed approach [1] to describe the stochastical behaviour of phase locked loops (PLL) to compare the performance degradation of...
For next-generation wireless networks, massive multiple-input multiple-output (MIMO) promises significant performance gains compared to today's wireless communication standards. In this paper, we address the challenge of how to synchronize the carrier signals of all antenna units in a large network. We show that mutually coupled digital phase-locked loops (DPLLs) can enable in-phase synchronous clocking...
We adopt the power gain description of wireless networks in order to provide conceptual insights on existing distributed asynchronous beamforming algorithms. From this common viewpoint, we compare the asynchronous distributed pricing (ADP) algorithm and the asynchronous scaled gradient projection (SGP) algorithm in terms of local subproblems, required information exchange and convergence behavior...
Cellular networks with a dense reuse of spectrum strongly suffer from intercell interference (ICI). By coordinating the resource allocations (RA) of the individual base stations (BS) the ICI can be effectively mitigated. Since centralized ICI coordination schemes become prohibitive in large-scale networks, we propose a decentralized RA procedure that coordinates the local RA steps among the BSs. Our...
We consider cooperating base station systems where the users are not aligned in time and frequency to the core network as it is actually desired for coherent joint signal processing. As it is widely known, time and frequency offsets can cause inter-symbol as well as inter-carrier interference in OFDM systems which leads to a reduced transmission performance. In this paper we investigate uplink joint...
We explore the opportunities in cellular system design and operation offered by the joint resource allocation of the space/frequency division multiple access (SDMA/FDMA) in uplink cooperative multi-point (CoMP) systems. First, we analyze the underlying combinatorial structure of the allocation problem in terms of user set partitions and permutations. Due to the exponential complexity we propose a...
Abstract-We present a simple but efficientalgorithm that iteratively refines the channel estimate in a turbo equalizer exploiting soft feedback (a-posteriori likelihoods) from the decoder. This algorithm, denoted as 'Soft Interference Cancelation and Correlation' (SICC), repeatedly performs an interference cancelation step followed by correlation with symbol estimates derived from the output of the...
We show that a general very simple relation holds between the variance of the unconditional and the mean of the conditional expected bit: both are identical for channels that are symmetric and in addition possess the property of exponential symmetry (also called consistency). Special cases are the binary erasure channel, the binary symmetric channel or the binary AWGN channel. This equality allows...
We consider a cellular network MIMO OFDM system where cooperating base stations apply joint signal processing to the receive signals of several users. In this situation, due to geometry, the problem of unavoidable differences in time of arrival between the users' signals occurs. As a result, symbol timing offsets can be larger than the cyclic prefix, which leads to OFDM inter-symbol interference....
It is well known that symbol timing offsets larger than the cyclic prefix between transmitter and receiver stations destroy the orthogonality among OFDM subcarriers inducing interblock interference by coupling subsequent OFDM symbols. In conjunction with MIMO transmission over frequency selective channels, this effect on top of multi-user interference strongly degrades performance. In this paper we...
We derive a relation between the unconditional and conditional (conditioned on the input bit X to be either 0 or 1) densities of the expected bit value, the so-called`soft bit' ??, given the log-likelihood ratios L(X) at the output of an AWGN channel. Both quantities are connected via the relation ?? = tanh(L/2). Denoting the unimodal, conditional soft bit density as f??lx,uni(??|x) and the bimodal...
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