Demodulation process for binary data

• US 5,287,516 A
• Filed: 11/26/1991
• Issued: 02/15/1994
• Est. Priority Date: 01/10/1991
• Status: Expired due to Fees

• Current Assignee: Landis & GYR Betriebs AG (Landis+Gyr Group AG)
• Original Assignee: Landis & GYR Betriebs AG (Landis+Gyr Group AG)
• Inventors: Schaub, Thomas
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Webster, Bryan E.
• Application Number:
  US07/798,618
• Time in Patent Office: 812 Days
• Field of Search: 329/300, 375/94, 375/95, 375/88, 375/91, 375/39
• US Class Current: 375/334
• CPC Class Codes: H04L 27/148 using filters, including PLL-type filters

Abstract

Two signals at different frequencies are optionally amplified or attenuated in an automatic gain control amplifier (1) after their reception, then separated from each other by means of band pass filters (2, 5) and amplitude-modulated by means of envelope curve detectors (3, 6), whereupon the envelope curve signals (z₀ [t], z₁ [t]) are sampled by means of sampling switches (4, 7) once per bit to produce sample values (z₀ [kT_b ], z₁ [kT_b ]) which are passed to a calculator unit (8) whose memory stores values of a decision table which are derived from a probability table. Each table area of the latter contains two probability values of which a first is the probability that the sample values (z₀ [kT_b ], z₁ [kT_b ]) lie in the respective table area if the first signal were sent and a second is the probability that the sample values (z₀ [kT_b ], z₁ [kT_b ]) lie in the respective table area if the second signal were sent. Set down in a table area of the decision table is a respective first logic value if the first probability value is greater than the second probability value and a respective second logic value if the first probability value is less than or equal to the second probability value. The process combines the advantages of the noncoherent demodulation process and the spread spectrum process.

Claims

1. A demodulation process for binary data which are transmitted by means of a frequency shift keying process by way of a transmission channel, wherein two shifted transmitted sinusoidal signals (s₀ (t), s₁ (t) of different frequencies (f₀, f₁), after reception, are first separated from each other in terms of frequency using bandpass filter means (2, 5) and then separately amplitude-modulated using envelope curve detection means (3, 6) for the purposes of producing two envelope curve signals (z₀ (t), z₁ (t)), characterized in that the values of the frequencies (f₀, f₁) of the two signals (s₀ (t), s₁ (t)) are selected to be so far apart that the latter are disturbed independently of each other and that at least one of the two frequencies (f₀, f₁) lies in a weakly disturbed frequency range of the transmission channel, that the two envelope curve signals (z₀ (t), z₁ (t)) are sampled once per bit using a sampling circuit means (4, 7) for the purpose of producing their sample values (z₀ (kT_b), z₁ (kT_b)), that the sample values (z₀ (kT_b), z₁ (kT_b)), are passed to a calculator unit (8) in whose memory values of a decision table are stored, which values are derived from the values of a probability table, that for the purposes of drawing up the probability table the value range of the sample values (z₀ (kT_b) and z₁ (kT_b)) of each respective envelope curve signal (z₀ (t) and z₁ (t)) is each in itself divided by means of threshold values (w₀,i with i=0,1,2, . . . , N₀ and w_ij with j=0,1,2, . . . , N₁) into a plurality (N₀ and N₁ respectively) of quantisation intervals which are plotted along respective ones of two coordinate axes of the probability table for the purposes of forming the table areas (i;

j) thereof, that for each table area (i;

j) of the probability table a first probability value (P₀ (i,j)) and a second probability value (P₁ (i,j)) is calculated and specified in the respective table area (i;

j), wherein the first probability value (P₀ (i,j)) is the probability that the sample values (z₀ (kT_b), z₁ (kT_b)) lie in the respective table (i;

j) if the first signal (s₀ [t]) were sent and the second probability value (P₁ (i,j)) is the probability that the sample values (z₀ (kT_b), z₁ (kT_b) lie in the respective table area (i;

j) if the second signal (s₁ (t)) were sent, that a first logic value ("0") representing the first signal (s_o (t)) is set down in a table area (i;

j) of the decision table which has the same threshold values (w₀,i, w₁,j) and as many (N₀.N₁) table areas (i;

j) as the probability table if the first probability value (P₀ (i,j)) is greater than the second probability value (P₁ [i,j]), and a second logic value ("1") representing the second signal (s₁ (t)) is set down if the first probability value (P₀ (i,j)) is less than or equal to the second probability value (P₁ (i,j)), and that the calculator unit (8) ascertains in which table area (i;

j) of the decision table the supplied sample value (z₀ (kT_b)), z₁ (kT_b)) lie, whereupon it is then deduced from the logic value ("0" or "1") contained in the respective table area (i;

j) of the decision table whether the first or the second signal (s₀ (t) or s₁ (t)) was most probably sent and is therefore to be considered as the received signal.

2. A demodulation process according to claim 1 characterized in that for the reception of signals (s₀ (t),s₁ (t) which are attenuated to different degrees, prior to the separation thereof in terms of frequency at the input of a receiver the most heavily attenuated signal (s₀ (t)) is so amplified using amplification means (1) and the most weakly attenuated signal (s₁ (t)) is so attenuated that both signals (s₀ (t), s₁ (t)) become at least approximately equal before they are separate from each other in respect of frequency.

3. A demodulation process according to claim 1 or claim 2 whereby the probability values (P₀ (i,j), P₁ (i,j)) contained in the probability table are stored in the memory of the calculator unit (8) in order for them to be taken into account in ascertaining the signal (s₀ (t) or s₁ (t)) which was most probably sent.

4. A demodulation process according to claim 1 or claim 2 whereby the logarithms of the probability values (P₀ (i,j), P₁ (i,j) contained in the probability table are stored in the memory of the calculator unit (8) in order for them to be taken into account in ascertaining the signal (s₀ (t) or s₁ (t)) which was most probably sent.