Scalable PLCP Header Extension within PSDU Abstract— Next generation UWB design needs additional header information fields than present in current ECMA-368 specification. However extending the ECMA-368 header beyond the available reserved bits while being compatible with legacy devices is a challenge. In this paper, we propose a scalable Physical Layer Convergence Protocol (PLCP) header extension within the Physical Layer Service Data Unit (PSDU) that allows for header extension beyond the reserved bits. The proposed mechanism also attempts to opportunistically convey the additional header information utilizing the padding bits present in the PSDU. Keywords- ECMA-368; PSDU; PLCP Header; Pad bits; FCS I. INTRODUCTION The PLCP Header in ECMA-368 specification [1] needs to be extended from its current form to accommodate more fields for next generation designs. There are some reserved bits in the PLCP Header but they are not sufficient to accommodate all conceivable extension header elements. An example can be channel state information (CSI) feedback that helps adaptive allocation of resources e.g. transmit power, modulation, coding etc. at the transmitter [2]. Other examples could be local link scheduling information or out of band control information. However extending the PLCP header beyond using reserved fields will not keep it compatible with legacy devices which cannot decode the new PLCP header and verify header check sequence (HCS). In this paper, we propose a scalable approach for header extension within the PSDU. This is usually suitable for • Information that is not needed to decode the current PSDU. • Non-critical information that does not need the additional robustness of PLCP header. The systematic part of the PLCP Header is sent at 39.4 Mbps because of the additional Reed-Solomon (RS) outer code while extension headers are sent at the payload data rate of at least 53.3 Mbps. • Information that can be sent optionally on a best effort basis if there is enough room in the PSDU. • Information that can be built up in an incremental way at the receiver over multiple frames when the full information does not fit within a single frame. In the current ECMA-368 specification, padding bits are inserted in the PSDU in order to align the data stream on the boundary of the symbol interleaver i.e. 6 symbols boundaries. We also explore the option of opportunistically sending the extension header elements by utilizing the padding bits in the PSDU without extending the frame duration. The extension headers are intended to serve as a low throughput feedback control channel incurring zero or minimal overhead. The control information in ECMA-368 can be sent in one of three ways – as beacon Information Element (IE), command or control frames, piggybacked with other traffic. Beacons can be sent once every 65.536 ms which may be less frequent than needed or/and may not have enough space available to accommodate the control information. On the other hand, control and command frames require separate Distributed Reservation Protocol (DRP) reservations and result in more overhead with separate preamble, header and inter frame spacing. Since each pair of transmitter and receiver requires separate DRP reservations for sending their frames, this method does not scale well with number of devices. Therefore piggybacking the control information with other data or control traffic is the preferred way. This can be improved further if we can accommodate the control information in the available padding bits of the piggy-backed PSDU. This is the main idea behind our proposed mechanism. It is to be noted that our approach needs no change to the PLCP preamble. The proposed header extension mechanism is generic enough to be applied in any system that has a common PHY and MAC header (e.g. PLCP Header of ECMA-368 and ECMA-387) with a limited number of reserved bits for the header extension. This is also suitable for systems with separate PHY and MAC headers with similar constraints for PHY header extension. The rest of the paper is organized as follows. Section II describes the existing ECMA-368 frame structure; section III describes the header extension proposals in detail while section IV concludes the paper. Soumya Das, Kaushik Chakraborty, Krishnan Rajamani, Özgür Dural and Samir S. Soliman Qualcomm Incorporated, San Diego, CA USA {soumyad, kaushikc, krajaman, odural, ssoliman}@qualcomm.com ICUWB 2009 (September 9-11, 2009) 9781-4244-2931-8/09/$25.00 ©2009 IEEE 570