1 / 22

A FREQUENCY HOPPING SPREAD SPECTRUM TRANSMISSION SCHEME FOR UNCOORDINATED COGNITIVE RADIOS

A FREQUENCY HOPPING SPREAD SPECTRUM TRANSMISSION SCHEME FOR UNCOORDINATED COGNITIVE RADIOS. Xiaohua (Edward) Li and Juite Hwu Department of Electrical and Computer Engineering State University of New York at Binghamton {xli, jhuw1}@binghamton.edu http://ucesp.ws.binghamton.edu/~xli. Contents.

Patman
Download Presentation

A FREQUENCY HOPPING SPREAD SPECTRUM TRANSMISSION SCHEME FOR UNCOORDINATED COGNITIVE RADIOS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. A FREQUENCY HOPPING SPREAD SPECTRUM TRANSMISSION SCHEME FOR UNCOORDINATED COGNITIVE RADIOS Xiaohua (Edward) Li and Juite Hwu Department of Electrical and Computer Engineering State University of New York at Binghamton {xli, jhuw1}@binghamton.edu http://ucesp.ws.binghamton.edu/~xli

  2. Contents • Introduction • System model • New FHSS transmission for cognitive radios • Demodulation and Performance analysis • Simulations • Conclusions

  3. Introduction • Cognitive radios (CRs) • Detect and utilize spectrum white spaces • Should avoid interfering primary users • A major issue: “Chicken-and-Egg Problem” • CRs are initially not synchronized (e.g., in picking spectrum) for transmission • Transmission is required to negotiate such synchronization • Our goal • Develop a transmission scheme for uncoordinated CRs, tolerable to spectrum/channel uncertainty and spectrum sensing errors

  4. Introduction (cont’) • Basic idea: Frequency-hopping over uncertain spectrum slots • CR transmitters and receivers hop over available spectrum slots • Hopping pattern determined by: • Spreading codes (shared) • Spectrum detection results (independent) • Channel selection rules (shared)

  5. Introduction (cont’) • Assumptions • CR transmitters and receivers do have • Some common spreading codes • A common channel selection rule • Common procedure of adapting transmission parameters, such as symbol rate, modulations, etc • CR transmitters and receivers do not • have common spectrum white space information

  6. 2. System model • Spectrum slots for frequency hopping • Divide the spectrum into I segments • Divide each segment into J frequency bands • Each band is a basic slot for frequency hopping, which we call “channel” • CR transmitters and receivers know slot structure, but do not know which slot is available in each time

  7. 2. System Model • Major problem • A channel may be available to a transmitter but unavailable to a receiver • Define parameters:

  8. 2. System Model Segmentation-based spectrum detection: When the CR transmits in a channel, it also collects information about the channels of next segment.

  9. 3. New FHSS transmission • Spreading • To transmit a sequence • Each symbol spreaded into M chips • This procedure is identical to CR transmitters and receivers

  10. Spectrum slot selection • Each chip is to be transmitted via a channel of ith segment Fi • Transmitters and receivers use a common binary sequence cn to determine channel selectability in this segment

  11. Channel selection rule • There may be many channels selectable in each segment • Each CR Tx or Rx needs to select one channel to transmit or receive • Distributed channel selection means Tx and Rx may choose different channels  synchronization problem • Smart channel selection rule can alleviate this problem • A simple rule: choose the first available channel of this segment • Secondary transmitter use fi,j1 if ui,j1=1 • Secondary receiver use fi,j2 if wi,j2=1

  12. Successful transmission→ Tx and Rx selected the same channel, i.e., j1=j2

  13. Illustration of multiple CR transmissions using our scheme

  14. FHSS/MFSK demodulation Vector symbol model for FHSS/MFSK signals 4. FHSS demodulation and performance analysis

  15. FHSS/MFSK received signal model Baseband channel matrix Frequency slot synchronization indicator function

  16. Element-wise description Coherent: Maximum Likelihood detection • Demodulations: coherent demodulation • Demodulations: non-coherent demodulation

  17. 4. FHSS demodulation and performance analysis • Performance analysis • Major issue: Tx and Rx may use difference frequency slots  channel mismatch • SNR for coherent demodulation

  18. Performance is limited by the correctness of frequency-selection • Assume mismatch probability pd be the probability that there is mismatch in the first j channels • With our simple channel selection rule

  19. Average channel mismatch probability • For every M transmissions, number of correct matches

  20. 5. Simulations Spreading gain M=40 Symbol amount K=100 Segments I=20 J=100 channels/segment

  21. 5. Simulation Mismatch pd≒0.1 Symbol amount K=100 Segments I=20 J=100 channels/segment

  22. 6. Conclusions • Developed an FHSS-FSK transmission scheme for uncoordinated cognitive radios • Tolerate spectrum sensing errors • No need of coordination assumptions • Use FHSS spreading gain to combat spectrum sensing errors and to avoid interfering primary users • Resolve the “chicken-and-egg” problem: provide a way for CRs to initiate communications in uncertain spectrum • Simulations demonstrate reliable performance even in large spectrum sensing errors

More Related