Conference Paper

Pre-RAKE diversity combination for direct sequence spread spectrum communication systems

Dept. of Electr. Eng., Keio Univ., Yokohama
DOI: 10.1109/ICC.1993.397307 Conference: Communications, 1993. ICC 93. Geneva. Technical Program, Conference Record, IEEE International Conference on, Volume: 1
Source: IEEE Xplore


A novel method of multipath diversity signal combination is
proposed for mobile direct sequence spread spectrum (DS-SS)
communications. Multiple transmissions are made for each spread signal.
Each transmission is independently delayed and amplified in the complex
domain according to the delay profile and the estimated path strength of
the channel. This is done to facilitate reception of a signal at the
mobile unit which is already a RAKE combination of the multipath
signals. This method is called a pre-RAKE combination system because the
RAKE combination function is performed pre-transmission. Using this
method the size and complexity of the mobile unit can be kept to a
minimum. The pre-RAKE method retains the advantages of diversity
reception in a multi-path fading environment. An examination of the SNR
for the traditional RAKE and the pre-RAKE systems and computer
simulations show that the performance of the pre-RAKE system is
equivalent to that of the RAKE system

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    • "ZF precoding often involves channel inversion, using the pseudo-inverse of the channel or other generalized inverses [4]. Matched filter (MF) precoding [8], similarly to the MF receiver, is interference limited at high SNR but it outperforms the ZF precoder at low SNR [4]. The regularized ZF precoder, as the name implies, introduces a regularization parameter in channel inversion. "
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    ABSTRACT: Linear precoding is a relatively simple method of MIMO signaling that can also be optimal in certain special cases. This paper is dedicated to high-SNR analysis of MIMO linear precoding. The Diversity-Multiplexing Tradeoff (DMT) of a number of linear precoders is analyzed. Furthermore, since the diversity at finite rate (also known as the fixed-rate regime, corresponding to multiplexing gain of zero) does not always follow from the DMT, linear precoders are also analyzed for their diversity at fixed rates. In several cases, the diversity at multiplexing gain of zero is found not to be unique, but rather to depend on spectral efficiency. The analysis includes the zero-forcing (ZF), regularized ZF, matched filtering and Wiener filtering precoders. We calculate the DMT of ZF precoding under two common design approaches, namely maximizing the throughput and minimizing the transmit power. It is shown that regularized ZF (RZF) or Matched filter (MF) suffer from error floors for all positive multiplexing gains. However, in the fixed rate regime, RZF and MF precoding achieve full diversity up to a certain spectral efficiency and zero diversity at rates above it. When the regularization parameter in the RZF is optimized in the MMSE sense, the structure is known as the Wiener precoder which in the fixed-rate regime is shown to have diversity that depends not only on the number of antennas, but also on the spectral efficiency. The diversity in the presence of both precoding and equalization is also analyzed.
    Full-text · Article · Feb 2012 · IEEE Transactions on Information Theory
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    • "Thus, certain kind of channel knowledge at the BS has a more significant impact on the performance as compared to SU-MIMO. The study initially started by assuming perfect channel knowledge at the transmitter and a number of references can be found in the literature, e.g., linear [4], [5], [6], [7] and non-linear processing [8], [9], [10], [11]. Again, realistic assumption on the channel knowledge at the transmitter is one of the key issues in commercial systems. "
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    ABSTRACT: This paper investigates multiple input multiple output (MIMO) transmission techniques based on realistic assumptions on feedback of channel state information. We consider three conventional techniques as the baseline: 3GPP long-term evolution (LTE) single user MIMO (SU-MIMO) based on implicit channel feedback, zero-forcing multiuser MIMO (ZF MU-MIMO) based on explicit channel feedback, and ZF MU-MIMO based on implicit channel feedback. SU-MIMO may not be able to exploit the full spatial dimension of the downlink MIMO channel. ZF MU-MIMO has the potential to improve the spectral efficiency, but the explicit channel feedback is not compatible with implicit feedback whereas implicit based ZF MU-MIMO is limited by performance and also the commonly assumed rank restriction makes it impossible to perform dynamic switching of SU/MU MIMO transmission. We propose a new hybrid scheme which enables such dynamic switching of SU/MU MIMO transmission by allowing UE to feed back the implicit channel information without any rank restriction. Computer simulation results show the benefits of the new hybrid scheme, which can properly switch to the better transmission mode in various correlation scenarios.
    Full-text · Conference Paper · Jul 2011
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    • "In fact, Direct Sequence Spread Spectrum (DS/SS) Code-Division Multiple- Access (CDMA) has emerged as the incoming standard for a variety of wireless communication systems, including the third-generation (3G) radio-mobile transmission technology [3] and the satellite systems [4]. It offers significant advantages in terms of channel capacity, mobile power consumption, link quality and resilience to multi-path propagation [5]. However, in order to exploit the advantages of a SS signal in a CDMA system, receivers must synchronize the local pseudo-noise (PN) code with the incoming PN code [6]-[7]. "
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    ABSTRACT: Satellite-based localization has attracted ever growing attention in the last few years. In this work, we present a signal processing technique for initial code acquisition and synchronization of satellite signals, such as the one used by position location techniques. Conventional approaches are based on the interpolation, usually carried out by (time-consuming) narrow-band over-sampling or (fast) fitting of few samples of a smoothed function of the ambiguity function around its coarse maximum. Conversely, the devised detector exploits a fast parabolic interpolation, running on three estimated ambiguity samples in the neighborhood of the coarse estimate. Performance analysis is carried out in comparison with the conventional power detector method. The obtained results have evidenced that the devised method is well suited for satellite spread-spectrum communications such as the GALILEO system.
    Full-text · Conference Paper · Apr 2010
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