Page scan

In the page scan substate, a unit listens for its own device access code for the duration of the scan window Tw page scan. During the scan window, the unit lis-tens at a single hop frequency, its correlator matched to its device access code. The scan window shall be long enough to completely scan 16 page fre-quencies.

When a unit enters the page scan substate, it selects the scan frequency according to the page hopping sequence corresponding to this unit, see Sec-tion 11.3.1 on page 135. This is a 32-hop sequence (or a 16-hop sequence in case of a reduced-hop system) in which each hop frequency is unique. The page hopping sequence is determined by the unit’s Bluetooth device address (BD_ADDR). The phase in the sequence is determined by CLKN_16-12 of the unit’s native clock (CLKN_15-12 in case of a reduced-hop system); that is, every 1.28s a different frequency is selected.

If the correlator exceeds the trigger threshold during the page scan, the unit will enter the slave response substate, which is described in Section 10.6.4.1 on page 105.

The page scan substate can be entered from the STANDBY state or the CON-NECTION state. In the STANDBY state, no connection has been established and the unit can use all the capacity to carry out the page scan. Before enter-ing the page scan substate from the CONNECTION state, the unit preferably reserves as much capacity for scanning. If desired, the unit may place ACL connections in the HOLD mode or even use the PARK mode, see Section 10.8.3 on page 114 and Section 10.8.4 on page 115. SCO connections are preferably not interrupted by the page scan. In this case, the page scan may be interrupted by the reserved SCO slots which have higher priority than the page scan. SCO packets should be used requiring the least amount of capac-ity (HV3 packets). The scan window shall be increased to minimize the setup delay. If one SCO link is present using HV3 packets and T_SCO=6 slots, a total scan window Tw page scan of at least 36 slots (22.5ms) is recommended; if two SCO links are present using HV3 packets and T_SCO=6 slots, a total scan win-dow of at least 54 slots (33.75ms) is recommended.

The scan interval T_{page scan} is defined as the interval between the beginnings of two consecutive page scans. A distinction is made between the case where the scan interval is equal to the scan window Tw page scan (continuous scan), the scan interval is maximal 1.28s, or the scan interval is maximal 2.56s. These three cases determine the behavior of the paging unit; that is, whether the pag-ing unit shall use R0, R1 or R2, see also Section 10.6.3 on page 101.

Table 10.1 illustrates the relationship between T_{page scan} and modes R0, R1 and R2. Although scanning in the R0 mode is continuous, the scanning may be interrupted by for example reserved SCO slots. The scan interval information is included in the SR field in the FHS packet.

During page scan the Bluetooth unit may choose to use an optional scanning scheme. (An exception is the page scan after returning an inquiry response message. See Section 10.7.4 on page 111 for details.)

10.6.3 Page

The page substate is used by the master (source) to activate and connect to a slave (destination) which periodically wakes up in the page scan substate. The master tries to capture the slave by repeatedly transmitting the slave’s device access code (DAC) in different hop channels. Since the Bluetooth clocks of the master and the slave are not synchronized, the master does not know exactly when the slave wakes up and on which hop frequency. Therefore, it transmits a train of identical DACs at different hop frequencies, and listens in between the transmit intervals until it receives a response from the slave.

The page procedure in the master consists of a number of steps. First, the slave’s device address is used to determine the page hopping sequence, see Section 11.3.2 on page 135. This is the sequence the master will use to reach the slave. For the phase in the sequence, the master uses an estimate of the slave’s clock. This estimate can for example be derived from timing information that was exchanged during the last encounter with this particular device (which could have acted as a master at that time), or from an inquiry procedure. With this estimate CLKE of the slave’s Bluetooth clock, the master can predict when the slave wakes up and on which hop channel.

The estimate of the Bluetooth clock in the slave can be completely wrong.

Although the master and the slave use the same hopping sequence, they use different phases in the sequence and will never meet each other. To compen-sate for the clock drifts, the master will send its page message during a short time interval on a number of wake-up frequencies. It will in fact transmit also on hop frequencies just before and after the current, predicted hop frequency.

During each TX slot, the master sequentially transmits on two different hop fre-quencies. Since the page message is the ID packet which is only 68 bits in length, there is ample of time (224.5 µs minimal) to switch the synthesizer. In the following RX slot, the receiver will listen sequentially to two corresponding RX hops for ID packet. The RX hops are selected according to the

page_response hopping sequence. The page_response hopping sequence is strictly related to the page hopping sequence; that is: for each page hop there is a corresponding page_response hop. The RX/TX timing in the page

sub-SR mode T_{page scan} N_page

R0 continuous ≥1

R1 ≤ 1.28s ≥ 128

R2 ≤ 2.56s ≥ 256

Reserved -

-Table 10.1: Relationship between scan interval, train repetition, and paging modes R0, R1 and R2.

state has been described in Section 9, see also Figure 9.4 on page 91. In the next TX slot, it will transmit on two hop frequencies different from the former ones. The synthesizer hop rate is increased to 3200 hops/s.

A distinction must be made between the 79-hop systems and the 23-hop sys-tems. First the 79-hop systems are considered. With the increased hopping rate as described above, the transmitter can cover 16 different hop frequencies in 16 slots or 10 ms. The page hopping sequence is divided over two paging trains A and B of 16 frequencies. Train A includes the 16 hop frequencies sur-rounding the current, predicted hop frequency f(k), where k is determined by the clock estimate CLKE_16-12. So the first train consists of hops

f(k-8), f(k-7),...,f(k),...,f(k+7)

When the difference between the Bluetooth clocks of the master and the slave is between -8x1.28 s and +7x1.28 s, one of the frequencies used by the master will be the hop frequency the slave will listen to. However, since the master does not know when the slave will enter the page scan substate, he has to repeat this train A N_page times or until a response is obtained. If the slave scan interval corresponds to R1, the repetition number is at least 128; if the slave scan interval corresponds to R2, the repetition number is at least 256.

Note that CLKE_16-12 changes every 1.28 s; therefore, every 1.28 s, the trains will include different frequencies of the page hopping set.

When the difference between the Bluetooth clocks of the master and the slave is less than -8x1.28 s or larger than +7x1.28 s, more distant hops must be probed. Since in total, there are only 32 dedicated wake-up hops, the more dis-tant hops are the remaining hops not being probed yet. The remaining 16 hops are used to form the new 10 ms train B. The second train consists of hops f(k-16), f(k-15),...,f(k-9),f(k+8)...,f(k+15)

Train B is repeated for N_page times. If still no response is obtained, the first train A is tried again N_page times. Alternate use of train A and train B is continued until a response is received or the timeout pageTO is exceeded. If during one of the listening occasions, a response is returned by the slave, the master unit enters the master response substate.

The description for paging and page scan procedures given here has been tai-lored towards the 79-hop systems used in the US and Europe. For the 23-hop systems as used in Japan and some European countries, the procedure is slightly different. In the 23-hop case, the length of the page hopping sequence is reduced to 16. As a consequence, there is only a single train (train A) includ-ing all the page hoppinclud-ing frequencies. The phase to the page hoppinclud-ing

sequence is not CLKE_16-12 but CLKE_15-12. An estimate of the slave’s clock does not have to be made.

The page substate can be entered from the STANDBY state or the CONNEC-TION state. In the STANDBY state, no connection has been established and

the unit can use all the capacity to carry out the page. Before entering the page substate from the CONNECTION state, the unit shall free as much capacity as possible for scanning. To ensure this, it is recommended that the ACL connec-tions are put on hold or park. However, the SCO connecconnec-tions shall not be dis-turbed by the page. This means that the page will be interrupted by the

reserved SCO slots which have higher priority than the page. In order to obtain as much capacity for paging, it is recommended to use the SCO packets which use the least amount of capacity (HV3 packets). If SCO links are present, the repetition number N_page of a single train shall be increased, see Table 10.2.

Here it has been assumed that the HV3 packet are used with an interval T_SCO=6 slots, which would correspond to a 64 kb/s voice link.

The construction of the page train is independent on the presence of SCO links; that is, SCO packets are sent on the reserved slots but do not affect the hop frequencies used in the unreserved slots, see Figure 10.5 on page 103.

Figure 10.5: Conventional page (a), page while one SCO link present (b), page while two SCO links present (c).

For the descriptions of optional paging schemes see “Appendix VII” on page 999.

SR mode no SCO link one SCO link

(HV3) two SCO links (HV3)

R0 N_page≥1 N_page≥2 N_page≥3

R1 N_page≥128 N_page≥256 N_page≥384

R2 N_page≥256 N_page≥512 N_page≥768

Table 10.2: Relationship between train repetition, and paging modes R0, R1 and R2 when SCO links are present.

SCO slot

SCO slots

a)

b)

c) 10ms train

1,2 3,4 5,6 7,8 9,10 11,12 13,14 15,16 1,2 3,4 5,6 7,8 9,10 11,12 13,14 15,16 1,2 3,4 5,6

3,4 5,6

1,2 3,4 7,8 9,10 13,14 15,16

1,2 5,6 7,8 11,12 13,14

5,6

3,4 9,10 15,16

1,2 7,8 13,14