Wireless optical communication system with adaptive data rates and/or adaptive levels of optical power

• US 5,808,760 A
• Filed: 09/03/1996
• Issued: 09/15/1998
• Est. Priority Date: 04/18/1994
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Gfeller, Fritz
• Primary Examiner(s): NEGASH, KINFE MICHAEL
• Application Number:
  US08/704,523
• Time in Patent Office: 742 Days
• Field of Search: 359/110, 359/152, 359/154, 359/143, 359/161, 359/172, 359/187, 340/825.72, 370/277, 371/20-21
• US Class Current: 398/27
• CPC Class Codes: H04B 10/1143 Bidirectional transmission

Abstract

The wireless optical (in particular infrared) communication system with at least one transmitter (75) and one receiver (76) comprises control means (77, 78), which dynamically adapt the data rate and/or the optical power of the transmitter in dependence of signal-to-noise ratio of the receiver. Due to this adjustment, optimized system performance is maintained even under the influence of ambient light which statistically changes the signal-to-noise ratio of the receiver. The best compromise between data rate, bit error rate and transmission range is dynamically determined. The control function is distributed between transmitting and receiving system unit. The control information is communicated via wireless optical communication.

Claims

1. A wireless optical communication system for data transmission with at least one transmitting unit for radiating modulated optical signals and at least one receiving unit for receiving said optical signals, characterized by control means comprising:

means to determine an optimized set of control parameters based on information reflecting the actual bit error rate provided by said receiving unit,

means for facilitating the optical wireless exchange of control data between said receiving unit and transmitting unit, and

means for dynamic adaptation of the data rate of said data transmission to ensure that said actual bit error rate does not exceed a predefined upper limit.

2. The communication system of claim 1, wherein the control means comprises at least one processor which receives information about said bit error rate of the data transmission from the receiving unit.

3. The communication system of claim 2, wherein the receiving unit comprises a transmitter for optical signals and the transmitting unit comprises a receiver for optical signals for exchanging said control data between said receiving unit and transmitting unit via wireless optical communication.

4. The communication system of claim 1, wherein the control means comprise at least two processors, one being part of the transmitting unit and one being part of the receiving unit, both communicating with each other for setting the data rate of the data transmission in an interactive process based on said control data exchanged.

5. The communication system of claim 4, wherein the processors communicate via bidirectional wireless optical communication.

6. The communication system of claim 1, wherein the control means includes at least one optical detector, which is used for determining the intensity of ambient light.

7. A wireless optical communication system for data transmission comprising:

at least one transmitting unit for radiating modulated optical signals,

at least one receiving unit for receiving said optical signals, the recieving unit having a detector for optical radiation which converts optical signals to electrical signals;

an amplifier and a bandpass filter for said electrical signals;

a signal averager which periodically samples incoming electrical signals during a time frame of a predefined duration T₁, and superposes said sampled signals of subsequent time frames m times, where m is a predefined integer; and

a decoding system for the extraction of the data from the signals after being processed by the signal averager, and

a control means having a means to determine an optimized set of control parameters based on information reflecting the actual bit error rate provided by said receiving unit, means for facilitating the optical wireless exchange of control data between said receiving unit and transmitting unit, and a means for dynamic adaptation of the data rate of said data transmission to ensure that said actual bit error rate does not exceed a predefined upper limit, the control means at least two processors, one being part of the transmitting unit and one being part of the receiving unit, both communicating with each other for setting the data rate of the data transmission in an interactive process based on said control data exchanged wherein the processors communicate via bidirectional wireless optical communication.

8. The communication system of claim 7, wherein the data rate is adapted by modifying the time per pulse T_p in combination with the corresponding modification of the electrical bandwidth B of the receiver in accordance with B≃

1/T_P.

9. The communication system of claim 8, wherein the data are split into subsets which are transmitted with k subsequent repetitions, where k is a predefined integer≧

1 and each subset has a predefined duration T₂.

10. The communication system of claim 9, wherein

the data rate is adapted by changing the number k of said repetitions according to predefined rules;

and

the signal averager and the decoding system are synchronized to the transmission of the packets, T₁ ≧

T₂ and k=m.

11. The communication system of claim 10, wherein

each subset carries n bits which are coded by pulse position modulation (PPM) within the duration T₂,

the receivers have means for decoding PPM-coded data.

12. The communication system of claim 11, wherein the data rate is adapted by changing n in combination with an adjustment of the optical power of the transmitting unit.

13. A method for wireless optical data communication between at least one transmitting unit and at least one receiving unit, comprising the steps of,

radiating optical signals from said transmitting unit;

detecting said optical signals by the receiving unit;

determining an optimized set of control parameters based on information reflecting the actual bit error rate of the transmission,

optically exchanging control data between said receiving unit and transmitting unit, and

dynamically adjusting the data rate of the transmission to ensure that said actual bit error rate does not exceed a predefined upper limit.

14. A method for wireless optical data communication between at least one transmitting unit and at least one receiving unit, comprising the steps of:

radiating optical signals from said transmitting unit;

detecting said optical signals by the receiving unit;

determining an optimized set of control parameters based on information reflecting the actual bit error rate of the transmission,

optically exchanging control data between said receiving unit and transmitting unit, and

dynamically adjusting the data rate of the transmission to ensure that said actual bit error rate does not exceed a predefined upper limit

converting the detected optical signals to electrical signal;

amplifying and filtering said electrical signals;

sampling said electrical signals during a time frame of predefined duration T₁ ;

averaging said sampled signals related to m subsequent time frames, m being an integer, and decoding said electrical signals.

15. The method of claim 14, wherein the step of adjusting the data rate comprises the step of modifying the time per pulse T_P in combination with changing the bandwidth B of the receiver in accordance with B≃

1/T_P.

16. The method of claim 15, wherein the data transmission is based on the steps of splitting up the data in subsets of duration T₂ and transmitting each subset with k subsequent repetitions, k being≧

1.

17. The method of claim 16, comprising the steps of

adapting the data rate by changing the number k of the repetitions according to predefined rules,

synchronizing the time frames for the sampling of signals with the subsets, and

averaging the sampled signals of m equivalent time frames.

18. The method of claim 17, wherein the data transmission entails the coding of n bits, n being an integer, by pulse position modulation (PPM) within each subset.

19. The method of claim 18, comprising the step of adapting the data rate by changing n in combination with an adjustment of the optical power of the transmitting unit.

20. A receiving unit for use in a wireless optical communication system comprising:

a receiver for optical signals,

means to determine the actual bit error rate,

means facilitating the optical wireless exchange of control data between said receiving unit and a remote transmitting unit, and

means to interactively determine an optimized set of control parameters taking into account information reflecting said actual bit error rate.

21. A receiving unit for use in a wireless optical communication system comprising:

a receiver for optical signals;

means to determine the actual bit error rate;

means facilitating the optical wireless exchange of control data between said receiving unit and a remote transmitting unit;

means to interactively determine an optimized set of control parameters taking into account information reflecting said actual bit error rate;

a detector for optical radiation which converts optical signals to electrical signals;

an amplifier and a bandpass filter for said electrical signals;

a signal averager which periodically samples incoming electrical signals during a time frame of a predefined duration T₁, and superposes said sampled signals of subsequent time frames m times, where m is a predefined integer; and

a decoding system for the extraction of the data from the signals after being processed by the signal averager.