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System Simulator >
System Component Models >
Demodulators >
Edge Demodulator (EDGEDEM)

Edge Demodulator (EDGEDEM)

Property	Description	Units	Default	Range/Type
DECISION	Hard{0}/soft{1} output selection	None	0	[0, 1]/Integer
RIN1	Input impedance	Ohm	Inf	(0, Inf]/Real
RIN2	Input impedance	Ohm	Inf	(0, Inf]/Real
ROUT	Output impedance	Ohm	0	[0, Inf)/Real
Ports
Input1	The FM modulated I-input signal (complex)
Input2	The FM modulated Q-input signal (complex)
Output	The output of FM demodulator (complex)

Notes

1. This element converts received I/Q signal stream into bit stream based on the EDGE 8PSK modulation. Each three output bits correspond to a pair of in-phase and quadrature input signals. Depending upon DECISION=0 or DECISION=1, the output can be either hard (e.g., 0,1,1,0,0,1,…) or soft (e.g., -0.21, 1.13, 0.82, -1.33, -0.78, 1.41, …). Performance can be maximized when the soft output in conjunction with channel coding are employed.

2. Let <q_n> be the estimated signal phase with removal of the additional phase shift q_{n., offset}, corresponding to the time index n. The hard-output decision rule (i.e., the mapping of <q_n> onto output bits) follows:

, ,

, ,

, ,

, .
In contrast with the hard-output demodulation, the soft-output demodulation uses a bit-by-bit decision rule called maximum a posteriori (MAP). For any given time index, let X = x_I + j ^. x_Q, |X| = 1, be a signal taken from the normal 8PSK signal set S, represent the binary bit triplet mapping onto a 8PSK signal, and Y= y_I + j ^. y_Q, be received baseband signal with removal of the additional phase shift. The soft-output value <b_k> (corresponding to b_k), k = 1,2,3..., is
given by

If the channel noise is AWGN, it can be proved that probability Pr(X|Y) in above equation can be expressed as

,
where Cis a constant, a is received signal amplitude and s²denotes the noise power. For simplification, factor α/σ²is not taken into account inside this demodulator, and ,b_k> is actually computed by using equation

which implies that, in the case that the channel is fading, the input signal should be weighted by instantaneous amplitudeto achieve better performance. Note that this modification in calculating the soft-output values will not degrade BER performance when a Viterbi decoder following the demodulator is used at the receiver.

Additional details about the EDGE 8PSK modulation can be found in [1]. For soft-output processing, refer to [2]-[4].

Netlist Form

EDGEDEM:Name n1 n2 n3 DECISION=val [Rin1=val], [Rin2=val], [Rout=val]

Netlist Example

EDGEDEM:1 1 2 3 DECISION=0

References

1. GSM 05.04 (i.e., ETSI EN 300 959): “Digital cellular telecommunications system (Phase 2+); Modulation”

2. R. Herzog, A. Schmidbauer and J. Hagenauer, “Iterative decoding and dispreading improves CDMA-system using M-ary orthogonal modulation and FEC.”

3. L. R. Bahl, J. Cocke, F. Jelinek and J. Ravivo, “Optimal decoding of linear codes for minimizing symbol error rate,” IEEE Trans. Inform. Theory, vol. IT-20, pp. 284-287, Mar. 1974.

4. H. H. Zeng, Y. Li and J. H. Winters, “Improved spatial-temporal equalization for EDGE: a fast selective-direction MMSE timing recory algorithm and two-stage soft-output equalizer,” IEEE Trans. Commun., vol. 49, pp. 2124-2134, Dec. 2001.

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