Space time coding in mimo
- 1. SPACE TIME CODING IN MIMO PRESENTED BY: ILA SHARMA 102001, MTECH ECE
- 2. OUTLINE • INTRODUCTION • MIMO • SPACE TIME CODE • ALAMOUTI CODE • APPLICATION OF MIMO • REFERENCES 17 April 2012 2
- 3. INTRODUCTION • Goal of modern wireless communication systems: - High Data Rates for Broadband, Video Conferencing etc. • Challenges to the goal: - Power, Bandwidth & Complexity. • Constraints to the goal: - To deal with noise - Multipath propagation - Interference 17 April 2012 3
- 4. MIMO • MIMO, is the use of multiple antennas at both the transmitter and receiver to improve communication performance. • MIMO exploits spatial diversity by having several transmit and receive antennas. • It can greatly increases the capacity of channels by independently sending streams of data across multiple antennas 17 April 2012 4
- 5. General MIMO 1 1 h11 h21 MT Transmit MR Receive antenna h12 h22 antenna 2. 2 . . hn2 . . . . h2m hn1 . . . h1m hnm MT MR Channel 17 April 2012 5
- 6. Contd… h h 11 12 .. h 1m H h h 21 22 .. h 2m .. .. .. .. h h n1 n2 .. h nm The received signal can be given as: y Hx n 17 April 2012 6
- 7. MIMO Benefits • High data rate • Achieve high channel capacity • Minimize probability of error • Bandwidth efficient. 17 April 2012 7
- 8. Introduction to Space-Time Coding • What is Space-Time Coding? • Space diversity at antenna • Time diversity • Why STC? • Maximum diversity • Maximum Coding Gain • Maximum possible throughput • Space-Time Block Codes: • These codes are transmitted using a block structure which enables simple decoding at the receiver. .
- 9. Alamouti Codes • Simple yet very effective • Space diversity at transmitter end At t1 At t2 X1, X2 X1 -X2* Symbol Transmit Ant1 bits Calculation Antenna X2 X1* Ant2 17 April 2012 9
- 10. Alamouti Code • Assume two transmit antennas and one receive antenna. • The space-time block code transmission matrix is x x* 1 2 G2 * x2 x 1 • For each pair of symbols transmit * * Antenna #1: x1 x2 Antenna #2: x2 x1 17 April 2012 10
- 11. CONTD ………. • The received signals are y1 h1 x1 h2 x2 1 * * . y2 hx 1 2 hx 2 1 2 • Calculate the decision variables as x1 ' h1* y1 h2 y2* * * x2 ' h1 y2 h2 y1 • Unfortunately, the technique is sensitive to delays. 17 April 2012 11
- 12. Summary of Alamouti’s Scheme • No feedback from receiver to transmitter is required for CSI to obtain full transmit diversity. • No bandwidth expansion (as redundancy is applied in space across multiple antennas, not in time or frequency). • Low complexity decoders. • No need for complete redesign of existing systems to incorporate this diversity scheme. 17 April 2012 12
- 13. Advantages and Disadvantages of Block STC • Advantages: – Space-time block coding utilizes multiple antennas to create spatial diversity, this allows a system to have better performance in a fading environment. – Good performance with minimal decoding complexity. – Can achieve maximum diversity gain – Receivers that use only linear processing. • Disadvantages: – Does not have much coding gain . – Can not always achieve the maximum data rates 17 April 2012 13
- 14. APPLICATIONS OF MIMO • Combined with OFDM, where the problems created by multi-path channel are handled efficiently. • MIMO gives reliable communication • MIMO increases capacity – MIMO uses independent channel fading due to multipath propagation to increase capacity. – No extra expensive bandwidth required 17 April 2012 14
- 15. REFERENCES • Hameed Jafarkhani, “Space-Time Coding-Theory & Practices”, 1st ed., Cambridge University Press. • V. Tarokh, H. Jafarkhani and A. R. Calderbank, “Space-time block codes for orthogonal designs,” IEEE Trans. Inform. Theory, vol. 45, pp. 1456–1466, July 1999. • V. Tarokh, N. Seshadri and A. R. Calderbank, “Space-time codes for high data rate wireless communication: performance criterion and code construction,” IEEE Trans. Inform. Theory, vol. 44, pp. 744– 765, Mar. 1998. • Ezio Biglieri, Robert Calderbank, Anthony Constentinicks, Andrea Goldsmith, Arogyaswami Paubraj, “MIMO Wireless communication”, 2nd edition, Cambridge University press,2007. 17 April 2012 15
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Editor's Notes
- #8: Array gain : improves resistance to noise, thereby improving the coverage and the range of a wireless networkSpatial diversity gain : mitigates fading and is realized by providing the receiver with multiple copies of the transmitted signal in space, frequency or time.Spatial multiplexing gain : The spatial multiplexing gain increases the capacity of a wireless network.Interference reduction and avoidance : It improve the coverage and range of a wireless network.
- #9: Space time coding is a method employed to improve the reliability of data transmission in wireless communication system using multiple transmit antenna.STCs rely on transmitting multiple , copies of a data stream to the receiver in the hope that at least some of them may survive the physical path between transmission and reception in a good enough state to allow reliable decoding.Space time codes(STC) provide transmit diversity for the MIMO.Achieve near optimal diversity gain.STC is concerned withMaximize the transmitted information rate.Minimize the error probability.