Apparatus and method for high-speed determination of received RF signal strength indicator

• US 4,868,885 A
• Filed: 05/05/1986
• Issued: 09/19/1989
• Est. Priority Date: 05/05/1986
• Status: Expired due to Term

• Current Assignee: Ericsson GE Mobile Communications Inc (Telefonaktiebolaget LM Ericsson)
• Original Assignee: General Electric Company
• Inventors: Perry, Fred G.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Kuntz, Curtis
• Application Number:
  US06/859,357
• Time in Patent Office: 1,233 Days
• Field of Search: 455/33, 455/62, 455/67, 455/52, 455/226, 455/12, 455/69, 455/10, 455/50, 455/53-56, 455/63, 455/68, 455/70, 379/59, 379/60, 364/811
• US Class Current: 455/10
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements

Abstract

Rapid measurement of the received signal strength indicator (RSSI) of a radio frequency signal is performed by sampling received signal amplitudes and averaging only selected ones of the sampled amplitudes. In one embodiment, two sample values obtained successively in time are compared and the larger of the two is stored, this process continuing over a desired sampling interval. Sampled values which exceed both the value obtained from an immediately preceding sample time and the value obtained from an immediately succeeding sample time are stored twice, while sample values which are less than immediately preceding and succeeding sample values are never stored. The stored values are averaged to yield an indication of average received signal amplitude. The resulting average value is very close to true average signal amplitude, is substantially unaffected by Rayleigh fading phenomenon, and yet is sensitive to rapid changes in received signal amplitude caused, for exaple, by obstacles in the signal transmission path.

Claims

1. A radio receiving device of the type including means for receiving a radio frequency signal subject to Rayleigh type fading effects on a radio frequency channel, said receiving device further comprising:

signal producing means operatively coupled to said receiving means for producing a first signal representing the instantaneous amplitude of said signal received on said radio frequency channel;

sampling means, connected to said signal producing means, for repetitively sampling the level of said first signal over a sequence of discrete time intervals to thereby produced a chronological sequence of sampled levels representing the instantaneous amplitude over time of said received radio frequency signal; and

control means, connected to said sampling means, for selecting all sampled signal levels exceeding (a) sampled signal levels immediately before said selected sampled levels in said chromological sequence and/or (b) sampled signal levels immediately following said selected sample levels in said chronological sequence, and for producing an output signal responsive to said selected sampled signal levels which represents an average amplitude of said received radio frequency signal over time and is insensitive to said Rayleigh fading effects.

14. A device as in claim 1 wherein said control means selects any given sampled level M times, M being an integer within the range of 0≦

M≦

2.

2. A digitally-controlled receiving device comprising:

radio signal receiving means for receiving a radio frequency signal on a radio frequency channel, said radio frequency signal being subject to Rayleigh fading effects, and for continually producing, at an output thereof, a first signal indicating the amplitude of said radio frequency signal on said radio frequency channel;

digital memory means, connected to receive said first signal, for storing a sequence of values of said first signal associated with a corresponding sequence of discrete time intervals; and

digital control means, connected to said memory means, for averaging the ones of said stored first signal values indicating amplitudes which exceed at least one of the stored first signal values prior to said selected signal values in said sequence and the stored first signal values following said selected signal values in said sequence and for providing a resulting average which is insensitive to said Rayleigh fading effects.

15. A device as in claim 2 wherein:

said control means accumulates a sum and calculates an average in response to said sum, and

said control means adds none of said stored signals to said sum more than twice, and does not add at least one of said stored signals to said sum.

3. A method of determining the average amplitude of a radio frequency signal subject to Rayleigh fading effects comprising the steps of:

(1) measuring the instantaneous amplitude of a radio frequency signal;

(2) after a predetermined time period has elapsed since the signal amplitude was last measured, again measuring said instantaneous signal amplitude;

(3) storing a value representing the larger of the two signal amplitudes most recently measured by said steps (1) and/or (2);

(4) repeating said steps (2) and (3) at least once; and

(5) averaging the values stored by said storing step (3) to provide a value which indicates the average of said radio frequency signal amplitude and which is insensitive to Rayleigh fading of said radio frequency signal.

4. A method as in claim 3 wherein said repeating step (4) comprises the steps of repeating said steps (2) and (3) a predetermined number of times.

5. A method as in claim 3 wherein:

said repeating step (4) is performed continuously; and

said averaging step (5) includes the step of averaging only the last N values stored by said storing step (3), N being a predetermined integer.

6. A method of determining the average level of a radio frequency signal comprising the steps of:

(1) sampling instantaneous levels S₁ -S_N+1 of a radio frequency signal occurring at a corresponding series of discrete times t₁ -t_N+1, N being an integer;

(2) comparing a signal level Si sampled by said sampling step at a time t_i, t₁ <

t_i <

t_N+1, with a further signal level S_i+1 sampled by said sampling step (1) at a time T_i+1 immediately following said time t_i in said series, i being an integer;

(3) selecting the larger of the two sampled signal levels compared by said comparing step (2);

(4) repeating said comparing and selecting steps (2) and (3) for each of said sampled signal levels S₁ -S_N ; and

(5) averaging said levels selected by said selecting step (3).

7. A method as in claim 6 wherein said selecting step (3) includes the step of selecting any sampled signal level S_i no more than twice.

8. A method as in claim 6 wherein said selecting step (3) further includes the step of not selecting any sampled signal level S_i which is less than a signal level S_i-1 sampled at an immediately preceding time t_i-1 in said series and is also less than a signal level S_i+1 sampled at an immediately succeeding time T_i+1 in said series.

9. A method as in claim 6 wherein said sampling step (1) comprises the step of periodically sampling said radio frequency signal at a fixed sampling rate on the order of the rate of occurrence of Rayleigh fading of said radio frequency signal.

10. A method as in claim 6 wherein said sampling step (1) comprises the step of periodically sampling said signal a fixed number of times N+1 over a fixed time period.

13. A method as in claim 6 wherein said selecting step (3) includes the step of selecting at least one of said sampled levels S_i twice.

11. In a radio receiving device of the type including tunable radio frequency receiving means for receiving a radio frequency signal of a preset frequency and for producing an RSSI signal responsive to the instantaneous amplitude of said received signal, a digital signal processor connected to control said receiving means and programmed so as to perform the following functions:

tune said receiving means to a predetermined radio frequency;

sampling instantaneous levels S₁ -S_n+1 of said RSSI signal occurring at a corresponding series of discrete times t₁ -t_N+1, N being an integer;

compare a signal level S_i, for 1≦

i≦

N with i being an integer, sampled at a corresponding time t_i with a further signal level S_i+1 sampled at a corresponding time t_i+1 immediately following said time t_i in said series;

select the larger of the two compared sampled signal levels for each integer value of i, 1≦

i≦

n; and

output a digital signal responsive to the average of said selected levels.

12. A digitally-controlled receiving device comprising:

a radio signal receiving means for receiving a signal subject to Rayleigh fading effects on a first radio frequency over a period of time and for producing a successive sequence of digital signals indicating the amplitude of said signal received on said same first radio frequency at a corresponding sequence of successive discrete time intervals during said time period;

digital signal selecting means, connected to receive said sequence of digital signals, for selecting digital signals from certain time intervals, said selected signals exceeding at least one of;

(1) the digital signals corresponding to the time intervals prior to the certain time intervals, and (2) the digital signals corresponding to the time intervals following the certain time intervals; and

averaging means for averaging said selected signals to produce a result, said result indicating an average received signal strength of said radio frequency signal on said same first radio frequency, said average being insensitive to said Rayleigh fading effects.

16. A device as in claim 12 wherein said control means selects at least one of said stored signals twice, selects none of said stored signals more than twice, and does not select at least one of said stored signals.

17. A digital radio communications device including:

radio frequency receiving means for receiving a radio frequency signal subject to Rayleigh fading effects at a certain radio frequency;

sampling means connected to said receiving means for sampling the amplitude of said received signal a plurality of times to provide a sequence of successive sampled values; and

processing means connected to said sampling means for comparing the sampled values of each pair of adjacent-in-time successive sampled values in said sequence and for calculating an average received signal strength value based on sampled values which said comparisons reveal exceed corresponding adjacent-in-time sampled values, said calculated average received signal strength value being insensitive to said Rayleigh fading effects.

18. In a digital radio communications device of the type including a radio frequency receiver for receiving a radio frequency signal, a method of determining an average amplitude of said received radio frequency signal subject to Rayleigh fading effects comprising the steps of:

(a) sampling the amplitude of said received signal to provide a sampled amplitude of OLD VALUE;

(b) subsequent to said sampling step (a), again sampling the amplitude of said received signal to provide a further sampled amplitude NEW VALUE;

(c) comparing said NEW VALUE and OLD VALUE sampled amplitudes;

(d) selecting the one of said NEW VALUE and OLD VALUE sampled amplitudes said comparison reveals exceeds the other of said NEW VALUE and OLD VALUE sampled amplitudes;

(e) replacing said OLD VALUE sampled amplitude with said NEW VALUE sampled amplitude;

(f) repeating said steps (b)-(e) a plurality of times to provide a corresponding plurality of selected sampled amplitudes; and

(g) averaging said sampled amplitudes selected by said selecting step (d) to provide an average which is insensitive to said Rayleigh fading effects.

19. A method as in claim 18 wherein:

said selecting step (d) includes storing said selected sampled amplitudes in a memory; and

said averaging step (g) comprises averaging plural sampled amplitudes stored in said memory.

20. A method as in claim 18 wherein said repeating step (f) includes repeating said sampling step (b) at a rate on the order of the rate of occurrence of said Rayleigh fading in said received signal.

21. A method as in claim 18 wherein said repeating step (f) includes a periodically repeating said sampling step (b) at a fixed rate on the order of the rate of occurrence of said Rayleigh fading in said received signal.

22. In a digital radio communications device of the type including a radio frequency receiver for receiving a radio frequency signal to Rayleigh fading effects, a method of determining an average received signal amplitude of said received radio frequency signal comprising the steps of:

(a) sampling the amplitude of said received signal to provide a first sampled amplitude;

(b) subsequent to said sampling step (a), again sampling the amplitude of said received signal to provide a further sampled amplitude;

(c) comparing said first and further sampled amplitudes;

(d) selecting said further sampled amplitude if said comparing step (c) reveals said further amplitude exceeds said first sampled amplitude;

(e) selecting said first sampled amplitude if said comparing step (c) reveals said first sampled amplitude exceeds said further sampled amplitude;

(f) subsequent to said sampling step (b), again sampling the amplitude of said received signal to provide a still further sampled amplitude;

(g) comparing said further and still further sampled amplitudes;

(h) selecting said further sampled amplitude if said comparing step (g) reveals said further amplitude exceeds said still further sampled amplitude;

(i) selecting said still further sampled amplitude if said comparing step (g) reveals said still further sampled amplitude exceeds said further sampled amplitude; and

(j) averaging said sampled amplitudes selected by said selecting steps to provide an average which is insensitive to said Rayleigh fading effects.