6.2.9.3 Obtain uplink parameters

After synchronization, the SS shall wait for UCD message from the BS in order to retrieve a set of transmission parameters for a possible uplink channel. These messages are transmitted periodically from the BS for all available uplink channels and are addressed to the MAC broadcast address. The SS shall determine whether it may use the uplink channel from the channel description parameters.

The SS shall collect all UCDs which are different in their channel ID field to build a set of usable channel IDs. If no channel can be found after a suitable timeout period, then the SS shall continue scanning to find another downlink channel. The process of obtaining uplink parameters is illustrated in Figure 48.

The SS shall determine from the channel description parameters whether it may use the uplink channel. If the channel is not suitable, then the SS shall try the next channel ID until it finds a usable channel. If the channel is suitable, the SS shall extract the parameters for this uplink from the UCD. It then shall wait for the next DL-MAP message and extract the time synchronization from this message. The SS then shall wait for a bandwidth allocation map for the selected channel. It may begin transmitting uplink in accordance with the MAC operation and the bandwidth allocation mechanism.

The SS shall perform initial ranging at least once, per Figure 50. If initial ranging is not successful, then the next channel ID is selected, and the procedure restarted from UCD extraction. When there are no more channel IDs to try, then the SS shall continue scanning to find another downlink channel.

The SS MAC is considered to have valid uplink parameters as long as it continues to successfully receive the UL-MAP and UCD messages. If at least one of these messages is not received within the time intervals specified in Table 118, the SS shall not use the uplink. This is illustrated in Figure 49.

Reset T12

Start

Lost UL-MAP

Interval

Maintain

Uplink

Figure 48—Obtaining uplink parameters

Maintain

Uplink

Reset

Lost UL-MAP Reset T12

Interval

Uplink

Parameters

Invalid

Obtain

Uplink

Parameters

Figure 49—Maintain uplink parameters, single uplink case, ChID=i

6.2.9.4 Message flows during scanning and uplink parameter acquisition

The BS shall generate UCD and DCD messages on the downlink at periodic intervals within the ranges defined in Table 118. The BS shall generate UL-MAP and DL-MAP at intervals as specified in a particular PHY specification. These messages are addressed to all SSs. Refer to Table 60.

Table 60—Message flows during scanning and uplink parameter acquisition

Table 60—Message flows during scanning and uplink parameter acquisition (continued)

6.2.9.5 Initial ranging and automatic adjustments

Ranging is the process of acquiring the correct timing offset such that the SS’s transmissions are aligned to a symbol that marks the beginning of a minislot boundary. The timing delays through the PHY layer shall be relatively constant. Any variation in the PHY delays shall be accounted for in the guard time of the uplink PHY overhead.

First, an SS shall synchronize to the downlink and learn the uplink channel characteristics through the UCD MAC management message. At this point, the SS shall scan the UL-MAP message to find an Initial Maintenance Interval. The BS shall make an Initial Maintenance Interval large enough to account for the variation in delays between any two SSs (maximum round-trip propagation delay due to cell radius plus maximum allowable implementation delay).

The SS shall put together a RNG-REQ message to be sent in an Initial Maintenance Interval. The CID field shall be set to the noninitialized SS value (zero).

Ranging adjusts each SS’s timing offset such that it appears to be colocated with the BS. The SS shall set its initial timing offset to the amount of internal fixed delay equivalent to colocating the SS next to the BS. This amount includes delays introduced through a particular implementation and shall include the downlink PHY interleaving latency, if any.

When the Initial Maintenance transmission opportunity occurs, the SS shall send the RNG-REQ message. Thus, the SS sends the message as if it were colocated with the BS.

The SS shall first send the RNG-REQ at minimum power level, and if it is not successful, the SS shall resend it at the next Initial Maintenance transmission opportunity at one step higher power level until successful.

Once the BS has successfully received the RNG-REQ message, it shall return a RNG-RSP message addressed to the individual SS. Within the RNG-RSP message shall be the Basic and Primary Management CIDs assigned to this SS. The message shall also contain information on RF power level adjustment and offset frequency adjustment as well as any timing offset corrections.

The SS shall now wait for an individual Station Maintenance region assigned to its Basic CID. It shall now transmit another RNG-REQ message at this time using the Basic CID along with any power level and timing offset corrections.

The BS shall return another RNG-RSP message to the SS with any additional fine tuning required. The ranging request/response steps shall be repeated until the response contains a Ranging Successful notification or the BS aborts ranging. Once successfully ranged (RNG-REQ is within tolerance of the BS), the SS shall join normal data traffic in the uplink. In particular, state machines and the applicability of retry counts and timer values for the ranging process are defined in Table 118.

NOTE—The burst profile to use for any uplink transmission is defined by the Uplink Interval Usage Code (UIUC). Each UIUC is mapped to a burst profile in the UCD message.

The message sequence chart (Table 61) and flow charts (Figure 50 and Figure 51) on the following pages define the ranging and adjustment process which shall be followed by compliant SSs and BSs.

Table 61—Ranging and automatic adjustments procedure