Frequency look-ahead and link state history based scheduling in indoor wireless pico-cellular networks

Abstract

A method and apparatus of combating the problem of interference in master-slave time division duplex indoor wireless networks based on standards, such as the Bluetooth™ standard, is proposed. The method involves a frequency look-ahead scheme in frequency hopping systems, a scheme of monitoring states of master-slave wireless communication links through values recorded in link history counters, and a scheme of scheduling an appropriate slave unit and choosing a suitable packet size to overcome the effect of interfering sources, if any, in the pico-cell.

1. A frequency hopping time division duplex indoor wireless communication system comprising:
 a master unit having a processor and a first frequency selection unit for finding a current frequency on which to transmit and receive during a current time slot and at least a second frequency selection unit interfaced with said processor to look ahead at frequencies that are to be used in future time slots; and 
 a plurality of mobile stations communicating with said master unit. 
 
     
     
       2. The communication system recited in  claim 1 , wherein the first and second frequency selection units comprise combinatorial logic units to perform frequency hop selection according to predetermined standards. 
     
     
       3. The communication system recited in  claim 1 , wherein the processor in the master unit interfaced to the second frequency selection unit cooperate such that a frequency corresponding to a future time slot is obtained by the processor by providing binary information about a pico-cell related address bits and clock bits corresponding to the time slot. 
     
     
       4. A frequency hopping indoor wireless communication system comprising:
 a master unit and a plurality of slave units; 
 said master unit having a plurality of link state counters C(i,j), wherein the condition of wireless links between the master unit and a slave unit are recorded in link state counters provided one for each frequency of communication f j  between the master and the slave “I”. 
 
     
     
       5. The frequency hopping indoor wireless communication system recited in  claim 4 , wherein
 1. the link state counters are initially reset to zero, 
 2. a counter C(i,j) is incremented by one when the master unit finds that a current transmission/reception with reference to slave unit “i” on frequency f j  failed, and 
 3. the counter C(i,j) is reset to zero when the current transmission/reception with reference to slave unit “i” on frequency f j  is successful or when the count value exceeds a reset threshold T RESET . 
 
     
     
       6. The frequency hopping indoor wireless communication scheme recited in  claim 5 , wherein
 1) a transmission attempt is made to slave unit “i” on frequency f j  if a value of the counter C(i,j) is less than or equal to a threshold T TRANSMIT , and 
 2) no transmission attempt is made to slave unit “i” on frequency f j  if the value of the counter C(i,j) is greater than the threshold T TRANSMIT , and the counter C(i,j) is incremented by one. 
 
     
     
       7. A frequency hopping time division duplex master-slave indoor wireless communication system comprising:
 a master unit having a processor and a first frequency selection unit for finding a current frequency on which to transmit and receive during a current time slot and at least a second frequency selection unit interfaced with said processor to select frequencies to be used in future time slots; and 
 a plurality of slave units communicating with said master unit, said master unit having a plurality of link state history counters C(i,j), wherein the link state counters are provided one for each frequency of communication f j  between the master and the slave “i”, wherein 
 a) before transmission to a slave unit, the master unit obtains the frequencies corresponding to time slots which will be encountered in the immediate future, 
 b) if the link state history counter for a scheduled slave unit at an expected transmission frequency indicates that a transmission attempt can be made, the master unit proceeds to transmit to the slave unit at an appropriate packet size, 
 c) the master unit tries to choose another active slave unit, if any, for transmission if the link state history counter for the scheduled slave forbids transmission, 
 d) the master unit records the loss and gain of service by the slave units when transmission to slave units takes place in an order different from the regular scheduling order, and 
 e) if the link state history counter values of all active slave units are above a threshold T TRANSMIT , the master unit chooses a slave unit whose link state history counter has the lowest value, and decides on a packet size of one. 
 
     
     
       8. The frequency hopping time division duplex master-slave indoor wireless communication system recited in  claim 7 , wherein
 f) after a slave unit for transmission is chosen by the master unit based on a link state history corresponding to a frequency to be used in a first time slot after a last time slot used by a current slave unit, the master unit checks for transmission worthiness for the slave at the frequency corresponding to an n-th time slot for transmitting an (n−1) size packet, and chooses the highest packet size corresponding to which the link state history counter value is less than or equal to a threshold T TRANSMIT , and 
 g) if all frequencies corresponding different allowed packet sizes are such that the corresponding link state history counter values are above the threshold T TRANSMIT , the master unit proceeds to choose another slave unit for transmission. 
 
     
     
       9. A frequency hopping time division duplex master-slave indoor wireless communication system comprising:
 a master unit and a plurality of slave units, wherein 
 (a) every active slave unit monitors packet transmissions from the master unit and records the number of successful receptions by using goodness counters GC(i,j) for every slave unit “i” with reference to frequency f j , 
 (b) a slave unit increments a goodness counter GC(i,j) when a packet transmitted by the slave unit on frequency f j  is successfully acknowledged by the master unit, 
 (c) short-term link history is maintained by periodic transfer of goodness counter values from active slave units to the master unit, 
 (d) the master unit constructs a link state history table of counters after receiving values of goodness counters GC(i,j) from all the slave units and uses this information during a next scheduling period, 
 (e) goodness counters GC(i,j) are reset to zero by slave units after successfully transmitting their values to the master unit, and 
 (f) the goodness counters GC(i,j) are allowed to count up to the maximum value and stay there until reset. 
 
     
     
       10. The indoor wireless communication system recited in  claim 9 , wherein
 (g) from among the currently active slave units, a first slave unit for which a value of goodness counter GC(i,j) for the frequency of transmission f j  is greater than or equal to a minimum goodness threshold value T GOOD  is chosen for communication starting from a next transmission time slot of the master unit, 
 (h) if, however, none of the slave units' goodness counter values is greater than or equal to the threshold value T GOOD , the master unit chooses a slave unit with a highest value of the goodness counter and decides on a packet size of one, 
 (i) after the slave unit for transmission is chosen by the master unit based on goodness counter values, the master unit checks for transmission worthiness for the slave unit at the frequency corresponding to an n-th time slot for transmitting an (n−1) size packet, and chooses a highest packet size corresponding to which a goodness counter value is greater than or equal to the threshold T GOOD , and 
 (j) if all frequencies corresponding different allowed packet sizes are such that the corresponding goodness counter values are below the threshold T GOOD , the master unit proceeds to choose another slave unit for transmission. 
 
     
     
       11. A frequency hopping time division duplex master-slave indoor wireless communication system comprising:
 a master unit and a plurality of slave units, wherein 
 (a) a second level frequency look-ahead is performed by the master unit even before a packet from an addressed slave unit is received, and 
 (b) the second level look-ahead is performed by the master unit to determine the slave units and packet sizes to be used next corresponding to the different sizes of packet that might be transmitted by an addressed slave unit. 
 
     
     
       12. A frequency hopping time division duplex master-slave indoor wireless communication system as recited in  claim 11  wherein the master unit maintains an expected state of wireless links with reference to interference by using a table of counters whose values indicate goodness of links. 
     
     
       13. A communication device employing a frequency hopping sequence to communicate with other communication devices in a wireless communications system, the device comprising:
 a processor;   a first frequency selection unit coupled to the processor for determining a frequency to transmit or receive messages during a current time slot; and   a second frequency selection unit coupled to the processor for determining one or more future frequencies to transmit or receive messages during look-ahead time slots.   
     
     
       14. The communication device of claim 13, wherein the first and second frequency selection units comprise combinatorial logic units to perform frequency hop selection according to predetermined standards. 
     
     
       15. The communication device of claim 13, wherein the processor obtains a frequency corresponding to a future time slot by using binary information about a pico-cell related address bits and clock bits corresponding to the time slot. 
     
     
       16. A wireless communications system having a plurality of communication devices, comprising:
 a link state database for containing values representing link states of the plurality of communication devices;   a first communication device for updating the link state database in accordance with condition of messages exchanged between the devices of the plurality of communication devices; and   a device selection module having a predetermined rule operative to select a second communication device in accordance with values of the link state of the plurality of communication devices,   wherein the first and second communication device exchange messages if the value of the link state between the first and second devices is less than or equal to a predetermined transmission threshold.   
     
     
       17. The wireless communications system of claim 16, wherein a value of the link state of a communication device is incremented when the messages received from the communication device is absented or corrupted. 
     
     
       18. The wireless communications system of claim 17, wherein the value of the link state of the communication device is reset to a predetermined value when the value of the link state exceeds a predetermined reset threshold. 
     
     
       19. The wireless communications system of claim 17, wherein the predetermined value is zero. 
     
     
       20. The wireless communications system of claim 16, wherein a value of the link state of a communication device is reset to a predetermined value when messages received from the communication device is correct. 
     
     
       21. The wireless communications system of claim 16, wherein the predetermined value is zero. 
     
     
       22. The wireless communications system of claim 17, wherein the predetermined transmission threshold is less than the predetermined reset threshold. 
     
     
       23. The wireless communications system of claim 17, wherein the value of the link state of the second communication device is less than the predetermined transmission threshold. 
     
     
       24. The wireless communications system of claim 17, wherein the second communication device is the one having the smallest link state value that is less than a predetermined transmission threshold. 
     
     
       25. A wireless communications system having a plurality of communication devices, comprising:
 a global link state database for containing values representing link states of the plurality of communication devices;   a first communication device having a local link state database,
 wherein the local link state data database contains values representing link states with a second communication device of the plurality of communication device, 
 wherein the values of link states are updated in accordance with condition of messages exchanged with the second communication device, and 
 wherein the values of link states are transmitted in a predetermined time period; 
   a link state database update module for updating the global link state database with the information received from the first communication device; and   a device selection module having a predetermined rule operative to select a second communication device in accordance with the values of link states of the plurality of communication devices,   wherein the first and second communication device exchange messages.   
     
     
       26. The wireless communications system of claim 25, wherein a value of local link state of the first communication device is incremented when messages received or transmitted successfully. 
     
     
       27. The wireless communications system of claim 26, wherein the value of local link state of the first communication device is reset to a predetermined value when the value of the local link state is sent to the link state database update module. 
     
     
       28. The wireless communications system of claim 27, wherein the predetermined value is zero. 
     
     
       29. The wireless communications system of claim 25, wherein the second communication device exchanging message with the first communication device has a local link state value greater than a predetermined transmission threshold. 
     
     
       30. The wireless communications system of claim 25, wherein the second communication device exchanging message with the first communication device is the one having a largest local link state value that is less than the predetermined transmission threshold.