Note: Descriptions are shown in the official language in which they were submitted.
2140~29
~ WO 94/28651 PCT/US94/04894
METHOD AND APPARATUS FOR CONVEYING A
FIELD OF DATA IN A COMMUNICATION SYSTEM
Field of the Invention
. -
The invention relates generally to communication ~yslems
and more particularly to conveying fields of data in a
communication ~y~Lem.
Background of the Invention
Digital communication systems, such as time divisionmultiplexed (TDM) communication ~y~Lellls, require tran~mi~sion
on a given radio frequency (RP) carrier signal during timeslots.
2 0 Tran~mi~sion of voice information does not present a problem in
the ~y~L~lll since a particular coding rate (and consequently a time
duration) is chosen to sufficiently meet the time constraints of the
TDM timeslot. However, when large, multi-slot messages are
required to be transmitted during a timeslot where the timeslot
2 5 size is small in comparison to the message, problems are
introduced into the ~ysLt:llL. Since the messages typically are
generated at a particular layer of the communication system
(where a layer is a convenient separation between functions
pertaining to different levels of a communication ~y~Lem), typical
3 0 solutions involve a segmentation scheme at a particular layer (say
layer n) above the air intPrf~ce, or data link layer.
Such schemes are inadequate for two reasons. First, they
recode the original message into multiple data link layer
m~s~ges, each of size less than one timeslot. In order for a layer
WO 94/28651 PCT/US94/04894
2~ 2
at a receiving unit to reassemble the message, layer n information
is passed with each timeslot transmitted. Consequently, the
resulting number of bits that are required to be transmitted is
increased by the number of bits in a layer n header multiplied by
5 the number of segments (or timeslots) needed to transmit the
message. Second, if the layer n message fails to transmit correctly,
the layer n entity has no recourse but to retransmit the entire
message, including all of the timeslots required to transmit the
message. Since the timeslot channel is a high~bit error rate
10 environment, retransmission of the entire me~sage may, and
does, frequently occur.
The Pan-European Digital Cellular (PEDC) system
designated group special mobile (GSM) is a layered protocol which
attacks the above problem by only allowing a window size of one
15 to be used. This is essentially an acknowledge/no-acknowledge
protocol for control functions. In user data service applications,
GSM has a layer 2 function run from a subscriber unit to an
interworking function for data services. As such, it does not have
a true point-to-point layer 2 function which exists from the
2 0 subscriber unit to a base-site. Other communication ~y~lellls, such
as AMPS are not layered and as such lack the structure to permit
the flexibility necessary in today's complex communication
systems.
Thus, a need exists for a communication system which
2 5 transmits multi-slot messages in a high bit error rate
environment during a relatively small timeslot which does not
increase the number of bits to be tran~mitte~ and is not required to
retransmit an entire message when error occurs.
~ WO 94/28651 21~ 0 ~ 2 9 PCT/US94/04894
,~ 3 .
Brief Description of the Drawings
FIG. 1 generally depicts a communication system which
utilized to implement message segmentation in accordance with
S the invention.
FIG. 2 generally depicts a transceiver (transmitter/receiver)
utilized in the communication ~y~lelll of FIG. 1 which employs
message segmentation in accordance with the ill~/el,lion.
FIG. 3 generally depicts a series of frames conveyed for a
particular radio frequency (RF) carrier as utilized by the
communication ~y~Lel~l of FIG. 1.
FIG. 4 generally illustrates the structure of a frame utilized
by the communication ~ysl~m of FIG. 1.
FIG. 5 generally illustrates the structure of a downlink
l S timeslot utilized by the communication ~y~lell- of FIG. 1.
FIG. 6 generally illustrates the structure of a modified
downlink timeslot utilized by the communication ~y~lem of FIG. 1
in accordance with the invention.
FIG. 7 generally illustrates the structure of a modified
2 0 uplink timeslot utilized by the communication :~y~lel~l of FIG. 1 in
accordance with the invention.
FIG. 8 generally depicts the structure of the second control
information field of the modified downlink timeslot of FIG. 6 and
the modified uplink timeslot of FIG. 7 in accordance with the
2 5 invention.
FIG. 9 generally depicts segmentation of a field of data in
accordance with the invention.
FIG. 10 generally depicts recombination of segments of data
to produce a field of data in accordance with the invention.
FIG. 11 generally depicts an alternate embodiment of a
modified downlink timeslot in accordance with the invention.
WO 94128651 PCT/US94104894
~i4~
Detailed Description of a Plefelled Embodiment
The communication system splits layers, namely layer 2,
into an upper and lower sub-layer in accordance with the
S invention. The upper layer consists of normal layer 2 functions
such as address and flow control capabilities, which cover the
entire message with a message comprising one or more slots. The
lower-layer 2 would provide error detection and re-transmission
capabilities on a timeslot basis such that retransmission of a
1 0 segment of data is on a timeslot basis rather than on an entire
message basis.
FIG. 1 depicts a communication system 100 which may
beneficially employ the present invention. In the preferred
embodiment, the communication ~yslelll 100 is a time division
1 5 multiplexed (TDM) personal communication ~y~m (PCS). As
such, the primary intent of the PCS is to serve slow moving
and/or stationary receiving/tran~mitting units, for example units
103 and 106. Consequently, unit 103 is a mobile subscriber unit
utilized by a pedestrian while unit 106 is a fixed subscriber unit
20 which may be, for example, utilized as a wireless local loop
replacement For the sake of convenience, units 103 and 106 will
be (lesign~ted as subscriber units 103, 106 hereinafter.
FIG. 2 generally depicts a transceiver
(transmitter/receiver) 200 which may beneficially employ the
2 5 present invention. The upper half of FIG. 2 generally represents
the transmitter portion 204 of transceiver 200. In the ~lefelled
embodiment, base-sites 109, 112 and subscriber units 103, 106
employ transceiver 200 depicted in FIG. 2. Also in the ~lefer.ed
embo~iment, base-sites 109 and 112 are i-lent.ic~l As shown in
3 0 FIG. 2, during tr~n~mission, upper layer information 201 is
input into a segmentator 202 which segments a field of data
contained within upper layer information 201. A multiplexer,
MUX 203, multiplexes the segments of data produced by
WO 94/28651 2 1 4 0 0 2 9 PCT/l~S9411)4894
segmentator 202 to ready the segments of data for tr~n.~mi~sion
as shown in FIG. 9. Upper layer information (ULI) 201 consists
of ULI for timeslosts 0-9 as depicted in FIG. 9, but is shown as
only one input for convenience. Continuing, output of MUX 203
S is input into data input 206 which adds a second control
information field to each segment of data to be transmitted in the
user information field. The output of data input 206 is input into
a conventional modulator 212, up-converted in frequency by
mixer 218 and intermediate frequency (IF) signal 215, filtered by
1 0 IF 221 and eventually up-converted in frequency again by mixer
227 and local o.~ stor (LO) 224. The output of mixer 227 is input
into a conve~tio~l power amplifier, ~lesign~ted by power oul~llt
230, and transmitted to a receiving unit via a conventional
antenna 233. Controller 209 controls operation of segmentator
1 5 202, MUX 203 and also provides LO 224 to mixer 227. In the
preferred embodiment, controller 209 is a 68000 series
microprocessor by Motorola.
The lower half of FIG. 2 generally depicts the receiver
portion 234 of transceiver 200. As shown in FIG. 2, a signal 236
transmitted by a transmitter portion 204, is received by a
conventional ~ntenn~ 233 and input into RF input 235. RF input
235 contains typical front-end receiver equipment such as, inter
alia, duplexers, splitters, etc (not shown). The output of RF
input 235 is input into mixer 239 and is subsequently down-
2 S co~lve~ led by LO 242. The output of mixer 239 is filtered by IF 245,
whose output is then input into mixer 251 and again down-
converted by IF signal 248. The oul~ul, of mixer 251 is input into
demodulator 254 which demodulates this fiign~l Output from
demodulator 254 is input into a demultiplexer (DEMUX) 257
3 0 which b~.~ic~lly undoes the multiple~ing function perrorllled by
MUX 203 of transmitter portion 204. Output of DEMUX 257 is
actually output for each timeslot 0-9 as shown in FIG. 10, but is
shown as only one output in FIG. 2 for convenience. Contining~
output from DEMUX 257 is the transmitted segments of data
WO 94/28651 ~9 PCT/US94/04894
~Q~ 6
which are then input into recombiner 263 where they are
appropriately recombined to produce the original field of data.
Further detail is depicted in FIG. 10.
FIG. 3 generally depicts a series of frames conveyed for a
5 particular radio frequency (RF) carrier as utilized by the
communication ~ysLem of FIG. 1. The series of frames conveyed
for a particular RF carrier represent signal 236 shown in FIG. 2.
FIG. 4 generally depicts the structure of the frames depicted in
FIG. 3. Referring to FIG. 4, the basic structure of a frame 403 is
1 0 10 TDM timeslots 406 for each RF carrier, or cl~nnel. To
provide 32 Kbps speech at 500 slots per second, the RF çh~nnel
requires 500 Kbps capacity or 50 Kbps per timeslot in a 10
timeslot per frame configuration as depicted in FIG. 4. This
allows for 32 Kbps speech and its accompanying fields. Speech
1 5 coding is provided by Adapative Delta Pulse Code Modulation
(ADPCM) coder at 32 Kbps. In the ~lafe,led embodiment, the
time duration of a particular t.imeslot 0-9 of timeclot 406 are 200
microseconds which results in a frame 403 duration of 2
milliseconds.
2 0 FIG. 5 depicts a prior art representation of a downlink
t.imeslot 500 having a field of data consisting of at least control
information and user iL~oLl-,ation. As depicted in FIG. 5, 14 bits
represent bits for subscriber unit 103, 106 frame initi~li7~t.ion
and are represented by 501. Nine bits are found in control
2 5 information field 503, which in the ~,e~Iled embodiment is a
system control field. In the ~lefe~led embo~iment the nine bits
in control information field 503 are allocated as follows: (1) five
bits are used to represent 1 of 32 comhin~tions for a digital color
code utilized to represent a particular base-site; (2) one bit is
3 0 utilized to represent tr~ncmicsion of either user information or
control information; (3) one bit is utilized to represent that user
inform~tio~ transmitted is either voice or data; and (4) two bits
are utilized to represent segmentation control ("00" -
continll~tion slot, "01" - beginning slot, "10" - end slot, and "11" -
~ wo 94~28651 2 i 4 0 0 ~ 9 PCT/US94/04894
single slot). Continuing with reference to FIG. 5, 64 bits
represent user information field 506 and are utilized to transmit,
inter alia, speech, user data or robbed control data .~ign~ling,
and these bits correspond to a mllltiple~ed bit rate of 32 Kbps per
timeslot. Twelve bits 509 are for joint error detection and
synchronization by a receiving unit and a final single bit 512 is
utilized for power control of a power control ch~nnel (PCC).
FIG. 6 generally depicts a modified downlink timeslot 600
in accordance with the invention. Downlink timeslot 600 is
~imil~r to downlink timeslot 500 depicted in FIG. 5, however, a
second control information field 606 has been added to downlink
timeslot 600. In the preferred embodiment, first control
information field 603 is i(lent.ic~l to control information field 503,
and as such represents a system control field. Second control
1 5 information field 606 represents a segmentation control field.
FIG. 7 depicts a modified llplink t.imeslQt 700 likewise having a
second control information field 709 added thereon. The 56 bit
fields depicted in FIG. 6 and FIG. 7 represented by 609, 720 are
rem~inrlers of the user information field 506 initially discussed
2 0 in reference to FIG. 5. Second control information field 606, 709
is generally depicted in FIG. 8, with a set of comm~n(l.~ and
corresponding bit values disclosed in Table 1 below.
WO 94/28651 PCT/US94/04894
21~0~29
Frame Q"""a,~ R~ ses Encodina
8 7 6 5 4 3 2 1
u~ alionI (i~ur~ liûn) N(R)~F~ N(S) O
transfer
RR RR
(receive ready) (receive ready) N(R) F O 0
1~11 1 .
Supervisory not ready) (receiver N(R) / 1 0
not ready) F
REJ (reject) REJ (reject) N(R) / 1 0 0
F
SABM (set
asy~ ll unous O 0 1 P
balance mode)
DM (u'; conl~eul O O O F
Unnumbered
DISC
(di~conlle~;t) O 1 0 P O 0 1
UA (unnumbered
achl luJJlcd~e) O 1 1 F 0
FRMR (frame 1 0 0 F O 0
reject)
Table 1
5 In the preferred embodiment, second control information field
606, 709 is one of either a standard HDLC layered protocol or a
Lap B/Lap D protocol. The HDLC protocol is an ANSI standard
for the United States, while the LapB/LapD protocol is described
in CCITT Recommendation X.25 and is a European standard.
1 0 Second control information field 606, 709 occurs in every timeslQt
0-9 of timeslots 406 shown in FIG. 4. Consequently, when
information is passed from, for example, a base-site 109 to a
subscriber unit 103 (or vice versa), send/receive sequence
numbers are transferred back and forth on a timeslot basis
15 rather than an entire meSs~e basis.
WO 94/28651 214 0 0 2 9 PCT/US94/04894
.
An operational scenario flows in the following manner
from higher layers to lower layers. Messages are generated at the
User Application, Layer 3 or Layer 2 levels. If generated at the
User Application or Layer 3 level, they pass down to Layer 2 and
S are placed in a Layer 2 transmission buffer queue. The message
can also be generated at Layer 2, and as such would also be placed
in the transmission buffer queue. This transmission buffer queue,
in reality, consists of various priority queues that are sorted
according to message type and is located at data input 206 of
1 0 transmitter portion 204 of FIG. 2.
FIG. 9 generally depicts segmentation of a field of data in
accordance with the invention. As shown in FIG. 9, upper layer
information (ULI) 201 consists of ULI from timeslots 0-9 as
depicted in FIG. 4. ULI for each timeslot 0-9 is input into a
1 5 message formatter 903 for each particular timeslot. Output from
formatter 903 is input into segmentator 202 which the field of data
(ULI) into segments of data for tran~mi~sion in fields 609, 712.
MUX 203 multiplexes the segments of data into the remainder of
user information field 609, 712 such that the resulting "frame"
2 0 looks essentially like the frame of FIG. 4. In the preferred
embodiment, segmentator 202 segments the field of data, or ULI
into 56 bit segments of data. After MUX 203 multiplexes the
segments of data into a frame, data input 206 adds the lower layer
il.ro~ ation (LLI), represented by second control information field
2 S 606, 709 to the segments of data. The presence of second control
information field 606, 709 is transparent to the message
tran~mi~sion except in the case where some of the timeslots are
received in error. In such cases, the second control ilLfo.mation
field 606, 709 requests retran~mi~sions based on the information
3 0 content of a reject message. The length of the field of data (i.e. the
length of the message) is also transparent to second control
illfollllation field 606. Numbering of timeslots is contiguous over
message boundaries. For the last slot of a message, for example
WO 94/28651 5 PCT/US94/04894
~l4~
slot 908, and for single slot information messages, the "F" bit
disclosed in FIG. 8 in second control information field 606 is used
to indicate the opposite bit state of the last significant bit in the
timeslot. The remaining bits are fill bits. 'rhèrefore, if the "F" bit
5 is a "1", the fill bits are made up of "O"s. If the "F" bit is a "0", the
fill bits are "1"s. If the timeslot is exactl~r filled with the correct
number of bits, the "F" bit still has the opposite value of the last
bit in the message.
Recombination of segmented data of a field of data is
1 0 depicted in FIG. 10. DEMUX 257 demultiplexes the demodulated
timeslots into separate timeslots where data output 260 reads the
control information from second control information field 606,
709 (i.e. LLI 1003 of FIG. 10). The segmented data in user fields 609,
712 is input into recombiner buffer 263 where the segments are
1 5 stored until the entire message is received. Upon receiving the
entire message, mPss~ge formatter 1000 formats the segments into
the entire field of data. In this manner, each segment of data
transmitted in its own timeslot and having its own specific
control field, is recombined at a receiving unit to provide the field
2 0 of data.
In an alternate embodiment, the downlink timeslot may be
modified as that depicted in FIG. 11. As shown in FIG. 11,
alternate downlink timeslot 1100 has segmentation control 1103
removed from the 9 ~yslelll control bits and is now implemented
2 5 in second control information field 606, 709. The six remaining
bits are LapD control field 1106, which has essentially the make-up
of second control illfo~ ation field 606, 709 as shown in FIG. 8.
Two bits (one bit each from N(R) and N(S) of Table 1) from second
control information field 606, 709 of FIG. 8 are not utilized in
3 0 downlink timeslot 1100 depicted in FIG. 11, however operation as
a standard HDLC protocol or a LapD/LapB protocol is still
maintained.
WO 94/28651 2 1 ~ O 0 2 9 PCT/IJ594/04594
While the invention has been particularly shown and
described with reference to a particular embodiment and an
alternate embodiment, it will be understood by those skilled in
the art that various changes in form and details may be made
S therein without departing from the spirit and scope of the
invention.
