Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
  • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
  • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
  • H04B7/2643—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using time-division multiple access [TDMA]
  • H04B7/2656—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using time-division multiple access [TDMA] for structure of frame, burst

Definitions

• the present invention relates to multi-line wireless telephone systems. Description of the Related A r t
• a cordless or wireless telephone handset unit communicates via either analog or digital radio signals with a base unit, which is typically connected via a standard telephone line to an external telephone network. In this manner, a user may employ the wireless handset to engage in a telephone call with another user through the base unit and the telephone network.
• Multi-line wireless telephone systems are also in use in various situations, such as businesses with many telephone users. Such systems employ a handset that communicates with up to N handsets simultaneously, typically with digital communications schemes, such as time division multiple access (TDMA). It is desirable to implement the features of current private branch exchange (PBX) systems in a multi-line wireless telephone system.
• PBX private branch exchange
• Conventional multi-line wireless telephone systems typically must work within a specified bandwidth and modulation format, which thus constrains th e maximum capacity of the radio-frequency (RF) channel used to transmit signals between the base unit and the operating or active handsets .
• RF radio-frequency
• One problem that arises due to the fixed capacity or bandwidth available for such telephone systems and the inflexibility of such systems is that the available channel capacity may be inefficiently utilized when not all handsets are operating.
• channel capacity is selected so that all N handsets can operate simultaneously, if necessary.
• channel capacity is underutilized.
• Overall signal quality may be reduced in order to also reduce the total bandwidth (and thus the amount wasted when not all handsets are employed), but this reduces quality needlessly in some cases, for example where only one handset is operating and there is enough total channel capacity available to allow the single handset to communicate at high quality.
• a wireless telephone system comprises a base unit coupleable to one or more external telephone lines and having a base transceiver, and a plurality of wireless handsets which may be active or inactive.
• Each handset has a handset transceiver for establishing a time- division multiple access (TDMA) link, when said handset is active, over a shared RF channel with the base unit via the base transceiver.
• TDMA time- division multiple access
• each active handset communicates during an exclusive time slice of a TDMA scheme that allocates time slices to active handsets, wherein a number of data samples having a sample size are transmitted during each time slice.
• At least two handsets altematingly share a time slice, when one of said two handsets is to establish a new TDMA link and when establishing said new TDMA link would exceed the available channel capacity.
• Time slices are shared by reducing the sample size and thereby increasing the number of data samples transmitted during said shared time slices.
• Fig. 1 is a block diagram of TDMA multi-line wireless telephone system, in accordance with an embodiment of the present invention
• Fig. 2 is a schematic representation of the field, data packet, and audio packet structures used in the TDMA scheme of the system of Fig. 1;
• Fig. 3 is a table illustrating a variable- structure TDMA time slice allocation scheme used by the system of Fig. 1, in accordance with a n embodiment of the present invention.
• Fig. 4 is a table illustrating a fixed-structure TDMA time slice allocation scheme used by the system of Fig. 1, in accordance with a n embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT
• TDMA system 100 comprises a base unit 110, which has receiver and transmitter units 112 and 1 1 1 , respectively, and is coupled to external telephone network 116 via telephone line(s) 115.
• Base unit 110 also has a controlled microprocessor 113 for controlling and monitoring the overall functions of the base unit 110.
• System 100 also comprises N wireless handsets 120 j , 120 2 , . . . 120 N . Each has a transmitter and receiver unit (transceiver), such as transmitter 121 and receiver 122 of handset 120 , .
• receiver unit 112 comprises N separate logical receivers
• transmitter unit 111 comprises N separate logical transmitters, so that receiver and transmitter units 112 and 111 provide N total logical transceiver units, one for each of N wireless handsets.
• M handsets (0 ⁇ M ⁇ N) are operating (i.e., in the process of conducting a telephone call). Efficient power use is important for a wireless system since the handsets are typically battery-powered.
• sy stem 100 employs a digital TDMA scheme, as described in further detail below, which allows power to be efficiently used since each operating handset is "off (i.e., not transmitting or receiving data) most of the time, and is only "on" during its own “time slice” or slot.
• System 1 00 thus provides a wireless network between the base station 110 an d each handset 120 ; (1 ⁇ i ⁇ N).
• a TDMA scheme is employed th at allows available channel capacity to be more efficiently utilized. This is done by reducing the quality of two or more handset signals an d having them alternate each others' time slices, when a certain number of handsets are in operation, as explained in further detail below with reference to Figs. 2-4.
• a 2 ms field 210 of digital data comprises nine total packets, viz. a data packet 220 and eight audio packets such a s audio packet 230.
• Each data packet is a set of data transmitted either to a given handset from the base unit or vice-versa, during a discrete time slice during which time no other handsets receive or transmit data over the system's data channel.
• Each audio packet is a set of audio data transmitted either to a given handset from the base unit or vice-versa, during a given time-slice in an overall "epoch" scheme, again during which time no other handsets receive or transmit data over the system' s data channel.
• each type of packet contains various sub-fields o r sections.
• data packet 220 comprises a 32-bit sync field
• the data in data packet 220 is used to communicate between the base unit and a particular handset, and contains various types of information, such as caller ID type information, range an d power information, and the like.
• Audio packet 230 comprises an audio packet header 231 , FEC data section 232, and guard time 233.
• Audio packet header 231 for example, contains information identifying the audio packet (such a s the handset), the current place in the epoch, and the like.
• each handset receives 16 digitally compressed audio samples (such as ADPCM (adaptive differential pulse code modulation) samples) during each time slice of the epoch allocated for the handset to receive audio data; and transmits to th e base unit 16 ADPCM samples during each time slice of the epoch allocated for the handset to transmit audio data.
• ADPCM adaptive differential pulse code modulation
• ADPCM and related technical issues are described in detail in International Telecommunication Union (ITU), Recommendation G.727, ( 12/ 1990) , "5-, 4-, 3- and 2-Bits Sample Embedded Adaptive Differential Pulse Code Modulation (ADPCM),” http://www.itu.ch.
• Audio packet 230 therefore also comprises a main 64-bit "audio data" portion, which comprises either 16 4-bit ADPCM samples (high quality), or 32 2-bit ADPCM samples (low quality). The latter is th e case when more handsets are operating than can operate at high quality over the allocated maximum channel capacity of system 100.
• each handset in operation operates a t high quality when there are fewer than T handsets operating (calls i n place), where M ⁇ T and the maximum channel capacity is sufficient to handle up to T high quality calls or links simultaneously.
• M > T the maximum channel capacity is sufficient to handle up to T high quality calls or links simultaneously.
• the n selected pairs of handset channels are switched from high quality audio links to low quality audio links and alternate time slices.
• high quality (16 4-bit ADPCM samples per audio packet or time slice) provides 32Kbps ADPCM (the default audio data), and low quality (32 2-bit samples shared between two handsets, per audio packet) provides 16 Kbps.
• this embodiment of the present invention allows the maximum handset capacity at high quality to be doubled at low quality.
• up to 4 handsets m y conduct calls simultaneously at high quality, and up to 8 at low quality.
• Table 300 illustrating a variable-structure TDMA time slice allocation scheme epoch used b y system 100 of Fig. 1, in accordance with an embodiment of th e present invention.
• Table 300 contains N pairs of rows, one pair of rows for each existing handset. Each row is a field, such as field 2 1 0 of Fig. 2.
• N may b e greater than 8.
• N may be 12.
• Each row or field of the epoch may be referred to herein by the initial time slice or slot, which is used to transmit data (TD) to a given handset, or to receive data (RD) from a given handset.
• TD data
• RD data
• base unit 110 transmits data to handset #1 (e.g., handset 120 , of Fig.
• the time delay between data communication for a given handset 120; and the base unit 110 is thereby lengthened. This can cause, for example, a longer time delay or latency for causing a given handset to ring or to be apprised of caller ID information.
• a given handset polls at its specific data channel time slots for incoming calls and synchronization data from the bas e unit 110, and transmits audio packets over its specific data channel time slots when it initiates a call.
• the audio packet pairs e.g., TS1 , RS I
• each field 210 can carry one conversation using 32Kbps ADPCM, or two conversations using 16Kbps ADPCM (see ITU Rec. G.727).
• 16 4 -bit samples are transferred every 2ms each direction for a handset.
• system 100 implements the epoch of Table 300 as follows.
• they are assigned nominal numbers 1 through 4.
• both rows of each row pair u se the allocation shown by the top entry in the TD row, i.e. the entry not in parentheses.
• each audio packet time slice entry of Table 300 contains two entries.
• the top entry in TD rows or fields indicates th e "normal" allocation for the slot for both TD and RD rows, when M ⁇ T. This allocation is used for both TD and RD rows of a row pair. For example, if only 4 handsets are active (off hook), then, the sequence described above is followed, i.e. both the TD and RD rows follow th e sequence indicated by the top entry in the TD row.
• the bottom entry in parentheses, indicates the alternate allocation for the slot when M > T.
• the top entry indicates the normal alternating allocation when M > T. If a fifth handset (handset #5 ) becomes operative, there is not enough channel capacity to handle all 5 active or operative handsets at high quality. Therefore, handsets 1 and 5 share a time slice on alternate fields, and each audio packet doubles the number of samples it transmits during the time slice. For example, in this case, during the first audio packet time slice of row TDl, the entry TSl indicates that 32 2-bit audio ADPCM samples are transmitted to handset #1, instead of the usual 16 4-bit samples .
• the entry TS5 indicates that 32 2-bit audio ADPCM samples are transmitted to handset #5 during this time slice. Providing 32 2-bit ADPCM samples in the audio packets for handsets 1 and provides enough audio data for a 4 millisecond TDMA cycle.
• the system is dynamic, since, if handset #1 hangs up before handset #5, the base unit 110 can allocate 32Kbps to handset #5 for the remainder of the call. Depending on when handset #5 becomes active, the order can switch, so that the entry in parenthesis is applicable.
• system 100 may be said to be operating in a handset expansion mode.
• a total of 32 4-bit samples are transmitted to handset #1 every two fields (i.e., TS l a t high quality occurs twice).
• 32 2-bit (low quality) samples are still transmitted to handset #1 every two fields, except this is done in a single audio packet rather than in two.
• system 1 00 dynamically switches to handset expansion mode, and nominally numbers the newly-active handsets, which are then paired a s illustrated with others' time slices, as illustrated.
• handset #6 becomes active, it shares alternating time slices with ( and lowers the quality of) handset #2. In this case, we have:
• base unit 110 allocates transmit and receive slots to each subsequently active handset for audio transmission. If no handsets were in use, and handset 120 2 starts a call, transmit and receive slots TSl and RS I would be dedicated to handset 120 2 (i.e., handset #1) a t 32Kbps rate. Thus, for up to 4 active handsets, a high quality audio link of 32Kbps is provided for each handset. As the 5 th handset becomes activated, one existing channel is reduced to 16Kbps and th e 5 th handset is multiplexed into that channel with a 16Kbps rate. I f more than 8 handsets attempt transmission, they are blocked (all circuits busy signal).
• receiver unit 112 preferably comprises less than N separate receivers (preferably 8), and transmitter unit 111 comprises less than N separate transmitters (preferably 8).
• base unit 110 comprises a number of logical transceiver pairs equal to the maximum number of calls (links) that may b e established simultaneously.
• each active handset in normal mode, has fixed time slots for each field 210 (i.e. row of Table 300) for audio data transfer.
• the low quality handsets In expanded handset mode, the low quality handsets have fixed time slots for every other field 210 (i.e. row of Table 300) for audio data transfer.
• system 100 is adapted to dynamically r e - nominate handsets to optimize channel capacity usage. For example, suppose 6 handsets are operating as described above, and thus 4 of the 6 handsets are operating in low-quality mode. Next, suppose handsets #3 and #4 deactivate. At this point, it makes no sense for handsets #1 and #5 to share time slices or operate at low quality mode, since time slices for TS3, RS3, TS4, RS4 are not being used. Thus, system 100 in this case dynamically re-numbers or r e - nominates the four operating handsets as #s 1-4.
• TDMA is used to separate the data and audio into two channels, and to allocate bandwidth a s required to the handsets needing the channel.
• This technique is compatible with power saving protocols, since the data channel, which will always be available, is used to signal the handset and initiate calls.
• a specific time slot is provided for data for each handset, which is used to keep the TDMA in sync so that the handset transceiver communicates only during its designated time slice. Since the phones are battery operated, it is important that they transmit and listen only when they need to.
• the system 100 implements the epoch and scheme of Table 300 with a telephone system with 4 Plain Old Telephone System (POTS) lines (i.e., line 115).
• POTS Plain Old Telephone System
• line 115 With four dedicated POTS lines, one can always expect 32Kbps performance except when multiple handsets are in conference, or if some handsets are i n intercom while others are in line conversations.
• other line/handset combinations may be used.
• 2 transmit/receive pairs per audio data packet slot were used.
• the audio data samples could be reduced further in quality to transmit more samples per audio packet, to allow more than 2 handsets (e.g. 4) to share a time slice.
• a Table 400 illustrating a fixed- structure TDMA time slice allocation scheme epoch used b y system 100 of Fig. 1, in accordance with an embodiment of th e present invention.
• i n terms of adding additional handsets beyond the channel capacity there is less flexibility i n terms of adding additional handsets beyond the channel capacity.
• time slots are dedicated to each handset for both data an d audio.
• handsets #1 and #5 were the only handsets active, they would each be operating at 16Kbps ADPCM, even though there is additional bandwidth or channel capacity available.
• system 100 in implementing the epoch of Table 400 may dynamically re-nominate handset numbers to more efficiently utilize the available bandwidth.
• the wireless system described above according to the principles of the invention may be a cellular system where base unit 110 represents a base station serving one of the cells in a cellular telephone network.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Mobile Radio Communication Systems (AREA)
• Time-Division Multiplex Systems (AREA)

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• 1998
  • 1998-09-01 KR KR1020007006335A patent/KR100561930B1/ko not_active IP Right Cessation
  • 1998-09-01 CN CN98813602A patent/CN1121765C/zh not_active Expired - Fee Related
  • 1998-09-01 WO PCT/US1998/018090 patent/WO1999031827A1/en active IP Right Grant
  • 1998-09-01 AU AU90414/98A patent/AU9041498A/en not_active Abandoned

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