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.
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.
Space time coding in mimo
SPACE TIME CODING IN MIMO PRESENTED BY: ILA SHARMA 102001, MTECH ECE
OUTLINE• INTRODUCTION• MIMO• SPACE TIME CODE• ALAMOUTI CODE• APPLICATION OF MIMO• REFERENCES17 April 2012 2
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 - Interference17 April 2012 3
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 antennas17 April 2012 4
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 n17 April 2012 6
MIMO Benefits• High data rate• Achieve high channel capacity• Minimize probability of error• Bandwidth efficient.17 April 2012 7
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..
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* Ant217 April 2012 9
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 x117 April 2012 10
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
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
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 rates17 April 2012 13
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 required17 April 2012 14
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