Demodulator is comprised of hard demodulator and soft demodulator.
1.1 Basics of deinterleaver
The deinterleaver, which performs the inverse relation of interleaver, is also defined by two permutations.
The first permutation is defined by
i = s x floor(j/s) + (j + floor(16 x j/Ncbps)) mod s j= 0,1,..., Ncbps-1
s = max(Nbpsc/2,1)
The first permutation is defined by
k = 16 x i - (Ncbps -1)floor(16 x i/ Ncbps)
Here j is the index of the original received bit, i is the index after the first permutation, and k is the index after the second permutation.
1.2 Basics of soft-demapper
The Log-Likelihood Ratio(LLR) of decision bi,q is defined as LLR(bi,q) = log(P[bi,q =1| r[i])/P[bi,q =0| r[i])). In our design, a sub-optimal simplified LLR is utilized.
Therefore, LLR(bi,q) = (|Gch(i)|^2/4){min|y[i]-α|^2 - min|y[i]-β|^2}
α refers to the symbols with a '0' in position (I,k) and β is the complementary
2.1 Hard Demodulator
Hard demodulator includes 16QAM hard demodulator , QPSK hard demodulator and BPSK hard demodulator. 16 QAM hard demodulator consists of serilizer, deinterleaver and demapper. QPSK hard modulator consists of serilizer, deinterleaver and demapper. BPSK hard modulator merely consists of deinterleaver and demapper.
Parameters:
val bitsWidth: Int width of outputs
val dataWidth: Int width of inputs
val hsmod: Int hard demodulator and soft demodulator select signal
IO:
Inputs:
Val mod_ctrl: UInt ` modulation scheme control signal
val in.bits.iq: DspComplex input
val in.bits.pktStart: Bool package start signal
val in.bits.pktEnd: Bool package end signal
val in.valid: Bool valid signal
val out.ready: Bool ready signal
Outputs:
val out.bits.bits: SInt demodulated output
val out.bits.pktStart: Bool package start signal
val out.bits.pktEnd: Bool package end signal
val out.valid: Bool valid signal
val in.ready: Bool ready signal
Parameters:
val bitsWidth: Int width of inputs and outputs
val dataWidth: Int width of outputs
val hsmod: Int hard demodulator and soft demodulator select signal
2.2 Soft Demodulator
Soft demodulator includes 16QAM Soft demodulator , QPSK soft demodulator and BPSK soft demodulator. 16 QAM soft demodulator consists of serilizer, deinterleaver and demapper. QPSK soft modulator consists of serilizer, deinterleaver and demapper. BPSK soft modulator merely consists of deinterleaver and demapper. Our soft demodulation is based on sub-optimal simplified LLR, which significantly reduces the complexity of hardware and features negligible soft decoding performance loss.
IO:
Inputs:
Val mod_ctrl: UInt ` modulation scheme control signal
val in.bits.iq: DspComplex input
val in.bits.pktStart: Bool package start signal
val in.bits.pktEnd: Bool package end signal
val in.valid: Bool valid signal
val out.ready: Bool ready signal
Outputs:
val out.bits.bits: FixedPoint demodulated output
val out.bits.pktStart: Bool package start signal
val out.bits.pktEnd: Bool package end signal
val out.valid: Bool valid signal
val in.ready: Bool ready signal
Tests:
Include tests for bpsk, qpsk and qam16 hard and soft demodulator. Run testOnly modem.demodulatorSpec