Signal processing in a digital wireless radio can be divided into two parts: (i) baseband or digital processing, and (ii) RF or analog processing. For example, when we use BPSK modulation, in the baseband (digital domain) we turn each binary bit 1 to A (a digital number) and each binary bit 0 to -A. Then in the RF domain, we take this baseband signal to the carrier frequency and transmit it over the air, i.e., for binary 1 we transmit Acos(2fct) and for binary 0 we transmit -Acos(2fct). Here, fc is the carrier frequency.

Now, when we write y = h.x + n (with y as the received signal, x as the transmit signal, h as the channel coefficient between transmit and receive antennas, and n as noise) we are writing the equation in baseband (digital) domain. In other words, x is either A or -A and y is the received signal at the baseband (from which we try to guess x and the corresponding binary bit).

Question: Assume a two-antenna transmitter and a two-antenna receiver that uses spatial multiplexing to send two independent bit streams from each antenna. Assume a single carrier BPSK modulation with amplitude A=1. Let the channel coefficient between antennas for a given coherence time be: h(Tx Ant1, Rx Ant1)=1, h(Tx Ant2, Rx Ant1)=3, h(Tx Ant1, Rx Ant2)=3, h(Tx Ant2, Rx Ant2)=5. Assume that in the same coherence time, binary bit b1 is modulated and transmitted from Tx antenna 1 and binary bit b2 is modulated and transmitted from Tx antenna 2. Let the received baseband signals at Rx antenna 1 be equal to 2 and the received baseband signal at Rx antenna 2 be equal to 1. What are b1 and b2 bits?