Designing Low Power High throughput MAC for 802.11AD WLAN SoC Deepthi Vaibhav Rajapurohit Dr. Veena S Chakravarthi Asarva Chips and Technologies Bengaluru, India  The IEEE WLAN 802.11ad standard guarantees the multi giga bit throughput which is highest in the Wireless LAN (WLAN) technology.  The system designed for such high performance will pose enough design challenges to make them consume low power. Hence power management must be considered right from architecture to Physical Design stage.  The paper also talks about adopting low power management as an MAC sub-layer management entity (MLME) feature and a special control circuitry called Power Management Entity (PME) in the digital part i.e. at Medium Access Control (MAC) of the System on Chip (SoC).  PME manages power consumption of the logic considering the functionality and the configurations/modes.  Apart from the standard specific features, other low power options like power aware hardware partitioning, clock gating, power gating and switching selectively the blocks to low frequency etc. are supported in PME as applied to the WLAN MAC and other SoC blocks in data and control paths. Block level overview  The Host Block supplies the data packets from the higher layers of IP.  The Processor initializes, configures and controls all the modules based on the active requirement of a particular module.  The Processor configurations and Host data is conveyed to and fro the other data path modules through Host Interface block.  MAC is partitioned into MAC Software, MAC Hardware and PME. It controls all the protocol functions along with management of data-path. It also controls the power management by triggering power save configurations across the SoC.  Power Management Entity controlled by MAC block, is responsible for the trigger of power save techniques at appropriate times for the apt blocks.  Base Band (BB) – It constitutes a part of Physical (PHY) layer and it processes the data arriving from and destined to MAC. Power aware Hardware – Software partitioning Based on the functionality and response time to real time activities, SoC is divided into Hardware and Software. The critical functions like real time Tx – Rx switching, Power management entity Power Management entity is the smart block which enables the power save modes consecutively as per requirement. PME controls the major power hungry blocks which are available for function aware controls in WLAN 802.11ad SoC such as RF modules like Power Amplifiers, Base-band blocks like Control Physical layer, Single carrier Physical layer and OFDM physical layer blocks. It performs the protocol specified power save strategies and control the AP and STA's states by switching them into Active and Doze states based on the active interval. It also initiates clock and power gating enables to respective blocks with the knowledge of configuration and functional conditions. The power management strategies used in this paper are as follows. 1]IEEE WLAN 802.11 2012 standards and its amendments 2]NAPman: Network-Assisted Power Management for WiFi Devices 3]Low power consumption Intelligent Local Avoided Collision (iLAC) MAC protocol for WLAN”, 2012 IEEE International Symposium on Signal Processing and Information Technology  High performance WLAN 802.11ad MAC for WLAN SOC is designed with the mandatory low power management MLME feature as defined in the standard and in addition power management block also keeps optimal blocks active knowing the requirement as per the device configuration and functional mode.  This can provide power reduction roughly up-to 24 to 26% depending on the device configuration as Access Point and Station.  The strategy is extended to make the power management block smart by knowing the medium conditions, by automatic selection of the data path configurations.  Power management also controls the blocks in these configurations. The WLAN 802.11AD operates in the 60GHz band and uses wide channels of 2.16GHz to enable data rates up to 6.8Gbps The use of transmit beam-forming to ensure that the signal can be directed to the intended receiver for best signal to noise ratio (SNR). The standard also uses block acknowledgement (BA) policy at the MAC level to reduce the overhead of acknowledging each packet. Typical applications will be like high speed docking stations, AV streaming and multicasting, point to point data transmission with the radio serving as a high bandwidth cable replacement. Due to the high data rate the functional blocks will be operated in high frequency and hence results in high power consumption. To mitigate this, IEEE standard specifies low power management features to be implemented mandatorily but beyond this, design has to be deployed in many other low power design options to achieve additional competitive advantage. Authors are grateful to Asarva chips and Technologies for supporting the development work on WLAN SOC and encouraging us to publish the part of the work 1)Power management as MLME feature in Low Power MAC  The power save modes explained here allow a non-PCP/non AP STA to sleep at intervals negotiated with the PCP/AP.  Each non-PCP/non-AP STA can choose an independent wake up schedule that comprises its own power consumption and traffic queue requirements.  A STA under Power save mode can operate in two states: Awake – where the STA is fully powered or Doze where it cannot transmit or receive any frame and is in low power mode.  An AP/STA will buffer data frames addressed to other AP/ STAs in Doze state.  In Active Mode, STA is in the Awake state, except that the STA can switch to Doze state in an Awake BI when the STA is allowed to doze.  In Power Save (PS) mode, a STA alternates between the Awake and the Doze states. 2)Clock and Power gating based on active functionality  Power Gates are added at the appropriate blocks considering the context of the function and the settling time of the turning on to active modes.  For example, Power gating is done at RF modules like Power amplifier which is turned on only on need basis and then it is turned on so that the functionality complies with the standard specification. 3)MCS based power control  Based on the medium condition and the signal strength of the received packet and the bit/symbol error rate over a BI interval the modulation and coding scheme (MCS) is selected.  In case of management frames and control frame, Control PHY i.e MCS=0 is used to transmit and the response is expected with same MCS. So rest of the PHY's can be turned off till all the transaction is completed. 4)Smart data path configurations  Some smart configurations are also adopted such as a module switching to lower frequency when no heavy work is being executed by it. 5)Tx-Rx switching  In case of BTI interval, AP Till a receive activity is seen, the RX chain can be turned off for BTI Interval. As a STA, the TX chain can be turned off for BTI Interval. Data throughput and Power Consumption in different DUT configurations INTRODUCTION 802.11ad PROTOCOL RESULTS ANALYSIS CONCLUSION REFERENCES POWER MANAGEMENT INDICON 2016, IISc, BENGALURU 13 th INTERNATIONAL IEEE INDIA CONFERENCE INDICON 2016, 13th INTERNATIONAL IEEE INDIA CONFERENCE IISc, BENGALURU HIGH THROUGHPUT MAC  To enable high throughput of 6.8Gbps, multiple data packets are combined to form an Aggregated packet.  This feature when coupled with the BA mechanism and Additional PPDUs hopes to achieve the high data rates up to 6.8Gbps.  The medium time is divided into Beacon Intervals (BI), which in turn is divided into BTI, ABFT and DTI.  To fine tune the link and channel conditions between an AP and a STA, Beam forming procedure is followed by STAs.  The scope of this paper covers best sector selection at transmission end only, i.e. till Sector Level Sweep (SLS) phase. Receive is always Quasi Omni.  The best sector is selected by performing Beamforming under Sector Level Sweep(SLS).  All the management/data frames exchanged between those two pair of Initiator and Responder will now happen in the chosen Sector ID  This achieves the necessary Directional Multi- gigabit (DMG) link budget. . The process is re initiated on the expiry of beam link maintenance timer. Functions Host & Processor MAC BB Radio Power Consumption Initialization ON ON ON ON 100% Radio Caliberation ON OFF OFF ON 47% Scanning Host – OFF Processor -ON Tx – OFF Rx - ON Tx – OFF Rx - ON Tx – OFF Rx - ON 70% Beam forming Host – OFF Processor -ON Selectively turned ON Selectivel y turned ON Selective ly turned ON 68% Data Transmission / Reception Selectively turned ON Selectively turned ON Selectivel y turned ON Selective ly turned ON 84% Total power consumed 74% Power Saved 26% Average Power Computation, taking Radio Calibration as an example: During initialization, all the blocks, i.e. Host, Processor, Host Interface block, MAC, PME, BB, MSP and RF which in turn have multiple sub- modules inside them (19 modules in total) are ON and hence it consumes 100% power. Whereas, during Radio calibration, only Processor and RF blocks, where only 9 modules are turned ON. Hence, taking an average, the power consumed during Radio calibration is: (9/19)*100 = 47% The same calculation is extended in all sequences and an average of total power is obtained. Block Partitions with Power Controls  Radio block – This power hungry Analog block constitutes of Transmit and Receive chains.  Mixed Signal Processing (MSP) block – acts as an interface between Digital blocks at the back end and Radio at front end. management and control of data frames and control frames like Ready To Send (RTS), Clear to Send (CTS) are managed by MAC Hardware. Whereas, MAC software is designed to take up slower protocols like initialization, configuration, serving management frames like Beacon and Association frames. MAC hardware – software partition High throughput of 6.8 Gbps at Antenna is achieved by designing the SoC at a much higher throughput at the backend. With a clock frequency of 440 MHz and a bus width of 16 bits at MAC-PHY interface, double the throughput of around 14Gbps. To achieve this the incoming data is buffered depending on the number of clients accessing the data(around 28Gbps) Functions Host & Processor MAC BB Radio Power Consumption Initialization ON ON ON ON 100% Radio Caliberation ON OFF OFF ON 47% Scanning NA NA NA NA NA Beam forming Host – OFF Processor -ON Selectively turned ON Selectivel y turned ON Selective ly turned ON 73% Data Transmission / Reception ON Selectively turned ON Selectivel y turned ON Selective ly turned ON 84% Total power consumed 76% Power Saved 24%