Deliverable R4.1.5

1. Deliverable R4.1.5 CEFRIEL Roma – 24 Novembre 2005 MAIS adaptive and reconfigurable modem Giovanni Paltenghi

2. Table of Contents • MAIS Adaptive modem architecture • The Supervisor algorithm • Implemented simulator • Simulation results • Future work

3. MAIS Adaptive modem architecture • Approach: introduction in 802.16-2004 (WiMAX) baseband standard of a new architectural element (supervisor, SPV) performing optimization procedures • minimization of the transmitted power for a negotiated level of Quality of Service (appropriately translated at PHY layer) • SPV input • from MAC: Target BER and Target Bit-Rate (QoS parameters at PHY layer) • from PHY: channel state information (the set of the channel power gains |Hi|2) • access to internal look-up tables containing maximum bit-rates and error correction code gains for every RateID in AWGN channel • SPV output • to PHY: RateID, the number and the position of the ON SCs • to MAC: actual bit-rate and BER achieved

4. WiMAX • OFDM 256 subcarriers • bit-rate: up to 74 Mbit/s in 20 MHz channel channel model

5. The Supervisor algorithm (1) The aim of the MAIS SPV algorithm is to find the “optimum” choice of 1) the RateID (constellation size and channel code rate) 2) the number and the position of the active (ON) subcarriers and 3) the transmission power needed to fit the Target Bit Rate and the Target BER requirements with the “minimum” power constraint, given the current channel condition Example: current channel response

6. The Supervisor algorithm (2) Each RateID guarantees, for a given channel bandwidth, a maximum net bit rate that is achievable with all the subcarriers ON A look-up table containing maximum achievable net bit rates for all possible channel bandwidths in which the transceiver will work is pre-stored in the SPV 1 The SPV selects all the RateIDs that have an achievable bit rate greater than the Target Bit Rate required by the MAC SPV does not consider the RateIDs for which the maximum achievable bit-rate is less than the target one If there is not a single RateID that meets the requested Target Bit-Rate, the SPV informs the MAC that it is not able to fulfill the requirements. The MAC layer will then decide the next steps.

7. The Supervisor algorithm (3) For each useful RateID the SPV Calculates the minimum number of subcarriers that must be switched ON to satisfy the Target Bit Rate 2 3 Identifies the position of the Nj subcarriers which will be switched ON (the best possible choice is to select the Nj subcarriers that are less attenuated by the channel) 4 Reads form a pre-stored look-up table the SNR value that needs to be respected at the receiver by each subcarrier (treated as an AWGN channel) in order to achieve the required Target BER. From the SNR value the SPV estimates the subcarriers amplitude at the receiver, Aj, necessary to achieve the Target BER.

8. The Supervisor algorithm (4) For each useful RateID the SPV (cont’d) Pre-equalize the Nj active subcarriers of the OFDM symbol on the basis of the channel response, in order to obtain the requested amplitude value of Aj at the receiver (i.e. at the output of the channel) 5 Calculates the required total transmission power for the current OFDM symbol 6

9. The Supervisor algorithm (5) 7 Among all the useful RateID, the SPV chooses the one that requires the lower transmitted power Pj SPV prepares the OFDM symbol for transmission: • switches off the subcarriers that are not required • loads the active subcarriers with the selected RateID • multiplies all the active subcarriers by the proper amplitude Aij 8

10. Simulator: general features • number of simulation bits • downlink/uplink mode • guard interval • Eb/N0 range • channel model • IEEE 802.16-2004 OFDM baseband transceiver developed and tested with Matlab 6.5 • Full standard compliant • Flexible and reconfigurable

11. Simulation: scenario • To compare performances of standard and SPV transceivers, we measured the mean power transmitted by the two modems in different scenarios • For our simulation we tested the modems in seven different cases (indicated by the letters A, B, C, D, E, F, G), each one of them is related to a particular RateID (A->0, B->1, C->2, D->3, E->4, F->5, G->6), in the sense that the maximum bit rate achievable in one case is the bit rate permitted by the corresponding RateID • We supposed that modems can work in one of the seven cases at a time • Target Bit Rate randomly distributed between 0 and the maximum bit-rate achievable in the considered case • Target BER randomly distributed among values 10-4, 10-5 and 10-6. • The operations of the standard transceiver imply that OFDM symbols are always transmitted with a power that must guarantee the communication at the maximum bit-rate achievable by the chosen RateID and the minimum BER value requested by the MAC • Instead, the SPV adapts dynamically each OFDM symbol to the requests of the MAC (bit rate and BER) and to the measured channel response

12. Simulation Results: scenario C SPV requires 11.34 dB less transmitted power than the standard 802.16-2004 the standard transceiver requires a transmitted power of 32 dBm in order to achieve the required Target Bit Rates (it has to operate with RateID 2, the minimum RateID that guarantees the achievement of all the required bit rates) and BER When the required Target Bit Rate is low and/or the channel response is good (attenuation is low) and/or the required Target BER is high, SPV transmitted power can be significantly lower

13. Simulation Results