Coding for the Fading Channel: a Survey <s> Power control <s> The main focus of this presentation is adaptive down-link beam forming for PSK modulation based on subspace decomposition. A down-link beam forming algorithm with reasonable complexity is proposed which requires neither detection of other users' signals nor knowledge about the direction-of-arrival (DOA)s of the incident path components. The desired signal subspace is extracted from the composite space in cooperation with the optimal beam forming for uplink signal reception. <s> BIB001 </s> Coding for the Fading Channel: a Survey <s> Power control <s> We study the information outage rate of a block-fading Gaussian channel with strict delay constraint and constant rate transmission, under the assumption that both the transmitter and the receiver have perfect knowledge of the channel. We find the power allocation strategy minimizing the outage rate under a constraint on the average transmitted power. Numerical examples for the Rayleigh fading channel are provided. In particular, an explicit formula for the delay-limited capacity of the 2-block Rayleigh fading channel is derived. <s> BIB002 </s> Coding for the Fading Channel: a Survey <s> Power control <s> We study optimal constant-rate coding schemes for a block-fading channel with strict transmission delay constraint, under the assumption that both the transmitter and the receiver have perfect channel-state information. We show that the information outage probability is minimized by concatenating a standard "Gaussian" code with an optimal power controller, which allocates the transmitted power dynamically to the transmitted symbols. We solve the minimum outage probability problem under different constraints on the transmitted power and we derive the corresponding power-allocation strategies. In addition, we propose an algorithm that approaches the optimal power allocation when the fading statistics are not known. Numerical examples for different fading channels are provided, and some applications discussed. In particular, we show that minimum outage probability and delay-limited capacity are closely related quantities, and we find a closed-form expression for the delay-limited capacity of the Rayleigh block-fading channel with transmission over two independent blocks. We also discuss repetition diversity and its relation with direct-sequence or multicarrier spread-spectrum transmission. The optimal power-allocation strategy in this case corresponds to selection diversity at the transmitter. From the single-user point of view considered in this paper, there exists an optimal repetition diversity order (or spreading factor) that minimizes the information outage probability for given rate, power, and fading statistics. <s> BIB003 </s> Coding for the Fading Channel: a Survey <s> Power control <s> The paper presents a 4 states 1/3 code rate which uses Smile-Helical interleave TURBO code, the TURBO code has unequal error protection in different positions of the block information data, analyzes the reason of the unequal error protection and the distribution of the unequal error protection in one block information bits, and presents the BER result in the AWGN channel. <s> BIB004
Observation of BIB001 shows that what makes this Rayleigh fading channel differ from AWGN is the fact that R is a random variable rather than a constant attenuation. Consequently, if this variability of R could be compensated for, an AWGN would be obtained. This compensation can be achieved in principle if channel-state information is available to the transmitter, which consequently can modulate its power according to the channel fluctuations. Consider the simplest such strategy. The flat independent fading channel with coherent detection yields the received signal BIB001 . Assume that the channel state information R is known at the transmitter front-end, that is, the transmitter knows the value of R during the transmission (this assumption obviously requires that R is changing very slowly). Under these conditions, assume that the transmitted signal in an interval with length T is xt = s t; BIB004 where st has unit energy (equal-energy basic waveform) and is chosen under a given optimality criterion. One possible such criterion (constant error probability over each symbol) requires that = R ,1 : This way, the channel is transformed into an equivalent additive white Gaussian noise channel. The error probability is the same as if we had transmitted s over a channel whose only effect is the addition of n to the transmitted signal. The average transmitted power per symbol is then E x 2 t = E 1= 2 ; which might diverge. This technique ("channel inversion") is simple to implement, since the encoder and decoder are designed for the AWGN channel, independent of the fading statistics. For instance, it is common in spread-spectrum systems with near-far interference imbalances. However, it may suffer from a large capacity penalty. For example, in Rayleigh fading the capacity is zero. To avoid divergence of the average power (or an inordinately large value thereof) a possible strategy is the following. Choose = R ,1 if R R 0 R ,1 0 otherwise: BIB002 By choosing the value of the threshold R 0 appropriately we trade off a decrease of the average power value for an increase of error probability. The average power value is now  where p = P R R 0 . For an information-theoretic analysis of power-control techniques for the fading channel, see BIB003 .