This is an introduction of Next-Generation PHS technology, of which WILLCOM Corp. has just obtained the 2.5GHz radio frequency license as an officially recognized Broadband Wireless Access in Japan. Next-Generation PHS is a high-throughput huge-capacity telecommunication system that adopts both TDMA/TDD and OFDMA technologies. Inheriting the micro-cell and DCA (Dynamic Channel Assign) features of the existing PHS (advanced PHS included), Next-Generation PHS is developed as a more efficient and faster mobile technology that is to be commercialized in Japan soon.

The specification of Next-Generation PHS, titled A-GN4.00-01-TS Ver.01 Rev.02, and approved by the general meeting of PHS MoU Group in September 2007 is briefed in the following chapters. [Note : Latest version of Next Generation PHS specification is Ver.01 Rev.03 which was updated on October 2007.]

Specification of PHY Layer

Of the multiple access methods of Next-Generation PHS, OFDMA/TDMA method is adopted for DL (downlink), while OFDMA/TDMA and SC-FDMA/TDMA methods are adopted for UL (Uplink). Mixed use of OFDMA/TDMA and SC-FDMA/TDMA at UL stage is possible. The structure of a TDMA frame is symmetrical, with 4 slots at 625 us for UL and 4 slots at 625 us for DL. This structure, which is identical with that of the existing PHS, builds the mutual base for co-existence of the two PHS systems. TDD is adopted as the duplex method.

The following chart describes the major technical index used for Next-Generation PHS.

Duplex method	TDD
Downlink access method	OFDMA/TDMA
Uplink access method	OFDMA, SC-FDMA/TDMA
TDMA slot period	625 us
TDMA frame period	5 ms
Number of slots in one frame	8 slots, 4 slots for transmission and 4 slots for reception symmetrically

The following chart shows the OFDM parameter of Next-Generation PHS.

Parameter	Type 1	Type 2	Type 3	Type 4	Type 5	Type 6	Type 7
System Bandwidth [MHz]	2.5	5	10	10	20	20	20
Effective channel bandwidth [MHz]	1.8	3.6	8.1	9.0	16.2	17.1	18.0
Used subcarrier number	48	96	216	240	432	456	480
Subcarrier spacing [kHz]	37.5
Subchannel bandwidth [kHz]	900
Guard Interval length [us]	6.66 (For first OFDM symbol)
	3.33 (For other symbols)
OFDM Data length [us]	26.67
OFDM symbol length [us]	33.3 (For first OFDM symbol)
	30 (For other symbols)
Guard Interval ratio	1/4 (For first OFDM symbol)
	1/8 (For other symbols)
Total Guard Time [us]	51.67 (21.67 + 30)
OFDM symbol number per subcarrier	19

Specification of MAC Layer

Radio resource is managed and controlled in MAC layer of Next-Generation PHS by QS-Mode（high quality channel based on carrier-sensing mode）and FM-Mode（fast access channel based on MAP mode）. In QS-Mode, one PRU (Physical Resource Unit）will be assigned fixedly as a CSCH (Circuit Switching Channel) according to the result of carrier sense after an access request is received. As the assigned CSCH is occupied by one user at all times, it guarantees that this one user will be able to occupy a certain radio bandwidth too. Hence, QS-Mode is a perfect choice to carry out service that requires real-time voice communication when data occurs randomly.

In FM-Mode, one PRU will be assigned as a ANCH（Anchor Channel）according to the result of carrier sense after an access request is received. ANCH dedicated user control information as one user is assigned once. The PRU for communication assigns EXCH (Extra Channel) in every 5 ms according to MAP which contains information elements from ANCH. That is, EXCH is not exclusively taken by one user, but shared by multiple users. FM-Mode is a perfect choice to carry out high-speed data service as it holds the ability to correspond to the burst change of data amount swiftly.

By using QCS-ID（QoS Control Session Identifier）in Next-Generation PHS, providing multiple qualified services (eg: voice plus e-mail reception) to one user becomes possible.