Method and apparatus for a wireless local area network

A protocol for wireless local area network communication between a base stationary unit and a plurality of wireless terminals is disclosed. The main features of this protocol is based upon channel reservation requests by active wireless terminals. Contention is resolved and authorization is granted with data message signals transmitted by the authorized wireless terminal either immediately for asynchronous service or periodically for a time-based service. The system further provides for the base stationary unit to query the receipt of the data message signal by the wireless terminal authorized to receive the transmission. If no response signal is received, then the base stationary unit would authorize for itself transmission of the data message to relay it, either "over the air" or via wired connection to another base stationary unit in another data cell. The synchronous nature of the method provides for power saving by allowing the receiver and/or transmitter to be powered down during idle and other time slots.

TECHNICAL FIELD 
The present invention relates to a method and an apparatus to wirelessly 
communicate between a stationary base unit and a plurality of wireless 
terminals. More particularly, the present invention relates to a digital 
wireless system which can communicate between a stationary base unit and a 
plurality of wireless terminals in an asynchronous mode as well as a 
time-slotted synchronous mode, under the control of the base stationary 
unit. 
BACKGROUND OF THE INVENTION 
Wireless digital communication between a stationary base unit and one or 
more mobile wireless terminals is well known in the art. There are in 
general three types of transmission methods. In Frequency Division 
Multiple Access (FDMA), the available electromagnetic communication 
spectrum is divided into a plurality of frequency channels. Communication 
between the stationary base unit and one of the wireless terminals is 
affected over one of the frequency channels. Communication between the 
stationary base unit and a different wireless terminal is affected over a 
different frequency channel. In Time-Division Multiple Access (TDMA), 
transmission between a stationary base unit and a first wireless terminal 
is affected over a first "slice" in time. Transmission between the 
stationary base unit and a second wireless terminal is affected over a 
second "slice" of time, different from the first "slice". Finally, in Code 
Division Multiple Access (CDMA), communication between a stationary base 
unit and one or more wireless terminals is accomplished through spread 
spectrum transmission over a frequency range wherein a unique Pseudo Noise 
(PN) code distinguishes the communication between a stationary base unit 
and a first wireless terminal and a different PN code distinguishes the 
communication between the stationary base unit and a second different 
wireless terminal. See, for example, U.S. Pat. No. 5,267,244. 
The introduction and wide spread use of personal computers in the last 
decade has given rise to the need for interconnection of these personal 
computers. This has resulted in the need to design and to develop Local 
Area Networks (LAN) to interconnect the PC-based processing units. The 
prevalent LAN's are: Ethernet, where the stations are all connected onto a 
cable; and Token Ring, where all the stations are connected to each other 
in the form of a ring. Ethernet is based upon the concept of carrier 
sensing where all stations listen to the cable and only access the medium 
if it is idle. In Ethernet, however, since all the competing stations can 
access the medium at the same time, collision is possible. Thus, Ethernet 
must provide for collision detection and retry. Token-ring is based on 
each of the stations waiting for an access token which is passed in 
round-robin fashion. Since access to the transmission medium occurs only 
upon the receipt of the token, collision is avoided. However, the stations 
do have to wait for their assigned token. 
With the introduction of portable laptop and notebook computers and the 
merging of the computer with the wireless medium, such as radio frequency 
(as exemplified in cellular telephone networks), or infrared waves or 
other signals, there is a growing need for wireless connectivity for these 
portable computers. Wireless LAN's face a number of hurdles. These include 
restrictions on the allocation of frequency spectrum, limitations on the 
feasible data rates over the air, interference propagation, and power 
consumption. 
Furthermore, protocol such as Ethernet or token-ring are inadequate for 
wireless LANs for several reasons. First, with respect to Ethernet, it 
assumes that all stations can listen to one another, which may not be 
possible in the wireless case. Secondly, due to the introduction of 
multi-media applications, there is an additional requirement to support 
both asynchronous services (e.g. data) and time based services (e.g. 
voice). 
One prior an solution to the first problem, which is also known as he 
"hidden terminal" problem is to use a hub-based system, wherein all 
information exchanged between two wireless terminals is relayed by a hub 
or central stationary base unit. This is a waste of precious wireless 
bandwidth when the two wireless terminals are in range of one another. 
With respect to the second problem, the prior an has suggested 
partitioning the medium into two bands: one for asynchronous service and 
the other for time-based services, and providing independent protocol and 
controls for each of the two bands. This has now been codified in the 
United states by the FCC in its recent ruling on unlicensed Personal 
Communication Service (PCS). Asynchronous service requires the entire 
medium bandwidth for a burst duration and are tolerant to variable access 
delays, whereas time-based services require a fraction of the bandwidth on 
a periodic basis and are not tolerant of variable access delays. 
SUMMARY OF THE INVENTION 
Accordingly, there exists a need to provide a method and an apparatus for 
providing wireless communication between a plurality of wireless terminals 
or portable computing units, and a stationary base station, that can 
support both asynchronous communication and time-based services. As used 
herein, the wireless terminal can be any type of electronic device capable 
of transmitting and receiving digital data. This includes, but is not 
limited to, portable computers, digital cellular phones, digital modems, 
or any of the combination of the foregoing. The method provides 
transmitting periodically by the base station at the start of a first 
period of time (hereinafter "slot"), a synchronization signal and a status 
signal, transmitted over a period of time (hereinafter "initial period") 
measured from the commencement of said first slot. The synchronization 
signal is a clocking signal used by the wireless terminals to synchronize 
their operation. The status signal represents a command signal controlling 
the communication to or from the stationary base station. One of the 
wireless terminals transmits a request signal in a slot, after an initial 
period measured from the commencement of the slot. Thus, the slot can be 
the same as or different from the first slot. The request signal indicates 
the identity of the wireless terminal requesting subsequent transmission, 
the identity of one or more wireless terminals to whom the subsequent 
transmission is intended, the number of slots required for the subsequent 
transmission, and the frequency of the subsequent transmission signal. The 
base station responds to the receipt of this requested signal by 
transmitting at the start of a third slot, different from the first and 
second slots, a synchronization signal, a busy status signal, and an 
authorization signal, indicating the identity of the wireless terminal 
authorized to transmit, the identity of one or more wireless terminals 
authorized to receive, the starting slot and the number of slots for the 
required subsequent transmission. The base station subsequently transmits 
at the start of the starting slot, a synchronization signal and a reserve 
status signal. Whereupon immediately after the transmission of the 
reserved status signal, the wireless terminal transmits its data signal. 
A system to implement the foregoing method is also disclosed. Finally, a 
base station and a wireless terminal which has power saving features, are 
also disclosed.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring to FIG. 1 there is shown a graphical view of a plurality of 
communication cells 10(a-c). Within each communication cell 10 is an 
associated stationary base unit 20. The plurality of stationary base units 
20(a-c) are all connected to one another by a wired link 22, such as, by 
for example, a conventional Ethernet network or token ring network. 
Within each communication cell 10, the associated stationary base unit 20 
communicates wirelessly with a plurality of wireless terminals 30. As 
previously discussed, the wireless terminal can be any type of electronic 
device capable of transmitting and receiving digital data. This includes, 
but is not limited to, portable computers, digital cellular phones, 
digital modems, or any of the combination of the foregoing. In the 
preferred embodiment, digitally encoded RF signals are transmitted and 
received by the stationary base station 20 to one or more of the wireless 
terminals 30. 
Referring to FIG. 2, there is shown a schematic block level diagram of a 
wireless terminal 30. In general, the wireless terminal 30 comprises an 
RF/IF unit 24, an Analog Front End (AFE) 26, a Baseband Modem 28, an FEC 
Codec 29, and a Protocol & Control Unit (PCU) 80, whose components will be 
described in greater detail hereinafter. 
The RF/IF unit 24 performs the functions of carrier-to-baseband signal 
conversion, the I/Q modulation and demodulation, out-of-band interference 
rejection, waveform shaping, receive and transmit signal amplification, 
frequency synthesis, and antenna switching. 
The AFE 26 provides the digital-to-analog and analog-to-digital conversion 
between the RF/IF Unit 24 and the Baseband Modem 28. In addition, AFE unit 
26 performs associated anti-aliasing and reconstruction filtering. The 
digital-to-analog and analog-to-digital conversions are provided for both 
in-phase and quadrature-phase signals, each of which must be sampled at 
twice the PN code chip rate. 
The Baseband Modem 28 provides the functions of spreading and de-spreading, 
PN code generation, acquisition and synchronization, combining and message 
buffering. The Baseband Modem 28 handles many signal processing functions 
including the control of the RF/IF unit 24 and control logic for the modem 
blocks. 
The FEC Codec 29 implements the Forward Error Correction (FEC) encoder and 
decoder, which is used to improve the channel Bit Error Rate (BER). 
The PCU 80 implements the protocol of the communication which is the method 
of the present invention, controls the Baseband Modem 28, implements the 
power saving feature of the present invention, handles messages, and 
interfaces to the Network Interface Controller (NIC) for the higher 
protocol layers. 
Specifically and in greater detail, the wireless terminal 30 comprises a 
plurality of antennas 32(a-b), with one antenna 32a or the other antenna 
32b, used for transmitting and receiving, depending on which antenna 32a 
or 32b has the stronger received signal strength. The antennas are 
connected to a switch 34 which is controlled by an RF/IF control unit 36. 
The RF signal received by either antenna 32a or 32b, after passing through 
the switch 34, is supplied to a transmit/receive (T/R) switch 38. From the 
T/R switch 38, the received signal is supplied to a low noise amplifier 
40, (which may also include a filter). The signal is amplified (and 
filtered). From the amplifier 40, the amplified received signal is then 
supplied to a mixer 42 which converts the received amplified RF signal 
into an Intermediate Frequency (IF) signal. The conversion is based upon a 
difference frequency signal generated by a frequency synthesizer 44. The 
frequency selected by the frequency synthesizer 44 is based upon a signal 
supplied from a temperature compensated crystal oscillator 50 and is 
controlled by the RF/IF control unit 36. 
The output of the mixer 42 is then supplied to a second filter 46. The 
filtered IF signal is then amplified again by a second amplifier 48 whose 
gain is controlled by the RF/IF control unit 36. From the second amplifier 
48, the amplified filtered IF signal is then supplied to an I/Q 
demodulator 52 whose operating frequency is derived from the temperature 
compensated crystal oscillator 50, by passing through a multiplier 54. The 
outputs of the I/Q demodulator 52 are the analog I and analog Q signals. 
The analog I and analog Q signals is each supplied to a filter 56(a-b), 
respectively. From the filters 56, the analog I and analog Q signals are 
converted into a single interleaved digital signal by an A-to-D converter 
58, which produces the digital I/Q signal. 
The digital I/Q signal is then supplied to a Pseudo Noise Match Filter 
(PNMF) 60 which is controlled by the PN generator 62. PNMF 60 serves to 
de-spread the digital I/Q signal, with the PN generator 62 supplying the 
necessary PN (Pseudo Noise) code. The output of the PNMF 60 is supplied to 
an adaptive combiner 64 which serves to improve the signal to noise (S/N) 
ratio by combining multiple PNMF outputs. From the adaptive combiner 64, 
the signal is supplied to a differential decoder 66 which determines the 
received channel bit sequence. Finally, from the differential decoder 66, 
the signal is supplied to an FEC decoder 68. The FEC decoder 68 serves to 
correct for bit errors and produces the information bit sequence. 
From the FEC decoder 68, the signal is then supplied to a received block 
70. The received block 70 performs the function of interpreting the status 
signal. From the received block 70, the status signal is supplied to a 
control logic unit (CLU) 72 and other signals to the protocol and control 
unit 80. 
As will be discussed hereinafter, the receiver portion of the wireless 
terminal 30 also comprises a sync acquisition block 74 which locks onto 
the sync signal generated by the base station unit 20. The signal from the 
A to D converter 58 is also supplied to the sync acquisition block 74. The 
output of the sync acquisition block 74 is a signal which is supplied to a 
detect logic unit 76 which determines if a sync signal has been detected. 
From the detect logic 76, the signal is supplied to the CLU 72. 
The PNMF 60 is also in communication with the Steady State (SS) sync unit 
82 which serves to provide timing compensation and antenna selection. The 
SS sync 82 also receives the output of the temperature compensated crystal 
oscillator 50. In addition, the SS sync 82 is in communication with the 
CLU 72 as well as the PN generator 62. 
In the transmit mode, data is received by the protocol and control unit 80 
from the NIC, or from the rest of the digital system. The data is then 
supplied to a transmit block 90 which buffers the signal prior to 
transmission. The transmit block 90 is under the control of the CLU 72, 
which determines the transmission time based upon the received status 
signal. The output of the transmit block 90 is supplied to the FEC encoder 
92 which adds bits to the information bits for error correction. From the 
output of the FEC encoder 92, the signal is then supplied to a 
differential encoder 94. The differential encoder 94 determines the 
transmitted symbol sequence. The output of the differential encoder 94 is 
then supplied to an I/Q spread unit 96 which is under the control of the 
PN generator 62. The I/Q spread unit 96 spreads the signal. The signal 
from the I/Q spread unit 96 is then supplied to a D-to-A converter 98 
which produces the analog I and analog Q signals 100a and 100b 
respectively. The analog signals I and Q are each supplied to a filter 
102. From the filters 102(a-b), the analog I and Q signals are supplied to 
an I/Q modulator 104 which modulates the I/Q signals. The I/Q modulator 
104 modulates the I/Q signals based upon a carrier signal, whose frequency 
is supplied from the temperature compensator crystal oscillator 50 
multiplied by the multiplier 54. The modulated I/Q signal is then supplied 
to a variable attenuator 106, which performs the function of power 
control. The variable attenuator 106 is under the control of RF/IF control 
unit 36. From the output of the variable attenuator 106, the signal is 
supplied to a filter 108. From the filter 108, the signal is converted 
into an RF signal by the multiplier 110 which is under the control of the 
frequency synthesizer 44. The RF signal is then amplified by an amplifier 
112 and is then sent through the T/R switch 38 for transmission by the 
antenna 32a or 32b. 
Thus, from FIG. 2, it can be seen that the RF/IF unit 24 comprises 
amplifier 112, multiplier 110, filter 108, variable attenuator 106, I/Q 
modulator 104, low noise amplifier 40, mixer 42, second filter 46, second 
amplifier 48, I/Q demodulator 52, multiplier 54, temperature compensated 
crystal oscillator 50, frequency synthesizer 44, and the transmit/receive 
(T/R) switch 38. The Analog From End (AFE) 26 comprises filters 102(a-b), 
D-to-A converter 98, filters 56(a-b), and A-to-D converter 58. The 
Baseband Modem 28 comprises I/Q spread unit 96, differential encoder 94, 
transmit block 90, RF/IF control unit 36, PN generator 62, Steady State 
(SS) sync unit 82, Pseudo Noise Match Filter (PNMF) 60, adaptive combiner 
64, sync acquisition block 74, differential decoder 66, detect logic unit 
76, received block 70, and control logic unit 72. The FEC Codec 29 
comprises the FEC decoder 68, and the FEC encoder 92. Finally, the 
wireless terminal 30 comprises the Unit (PCU) 80. 
Referring to FIG. 3 there is shown a detailed block diagram of a portion of 
the wireless terminal 30 shown in FIG. 2. In FIG. 3, the schematic diagram 
shows the CLU 72 controlling the power to the wireless terminal unit 30. 
Since the wireless terminal 30 is a portable terminal, the power source is 
necessarily a cordless source, such as batteries. The status signal 
generated by the received block 70 is supplied to the CLU 72, along with 
the control signal from the PCU 80. In response the CLU 72 decodes the 
status signal and controls the power of the transmitter portion and the 
receiver portion in accordance with the following table: 
______________________________________ 
PCU 
Status Signal 
Control Signal 
Receiver Control 
Xmit Control 
______________________________________ 
IDLE REQUEST OFF ON 
BUSY -- ON OFF 
RES TRANSMIT OFF ON 
RES RECEIVE ON OFF 
______________________________________ 
The meaning of these signals will be explained in greater detail 
hereinafter. 
Referring to FIG. 4, there is shown one embodiment of a base stationary 
unit 20. The base stationary unit 20 is very similar to the wireless 
terminal 30. In block diagram form, the base stationary unit 20 comprises 
the two antennas 32a and 32b connected to a switch 34 which is controlled 
by an RF/IF control unit 36. The two antennas 32a and 32b perform the same 
functions as the two antennas for the wireless terminal 30. The signals to 
and from the antennas 32(a-b) are supplied by the RF/IF unit 24, which is 
the same as that described for the wireless terminal 30. The RF/IF unit 24 
is connected to the AFE unit 26, which is also the same as that described 
for the wireless terminal 30. A baseband modem 128 is also connected to 
the AFE unit 26. The baseband modem 128 is similar to the baseband modem 
28, except for the absence of the sync acquisition block 74 and the detect 
logic 76. In all other aspects, the baseband modem 128 is similar to the 
baseband modem 28. The FEC Codec 29 is similar to the FEC Codec shown and 
described for the wireless terminal 30. Finally, the PCU 80 is also 
similar to the PCU 80 shown and described for the PCU 80 of the wireless 
terminal 30. 
In the base stationary unit 20, the PCU 20 is connected to a host bus 102. 
A Network Interface Controller (NIC) 104 is also connected to the bus 102. 
The NIC 104 is connected to a Serial Network Interface (SNI) 106, which is 
also connected to a transceiver 108. Finally, the transceiver 108 is 
connected to the wired link 22, which is connected to other base 
stationary units 20, in other cells. 
In addition to the functions described heretofore for the PCU 80 operating 
in the wireless terminal 30, the PCU 80 in the base stationary unit 20 
performs the additional functions of maintaining a list of registered 
wireless terminals 30, a list of messages received over-the-air, if the 
message is broadcast or if the destination terminal is not in the 
registered list, then the message is sent over the host bus 102 to the NIC 
104. For messages that are received from the NIC 104, if the message is a 
broadcast or the destination wireless terminal 30 is in the registered 
list, then the message is transmitted over-the-air by the base stationary 
unit 20. The NIC 104 buffers the messages to and from the wired network 
and implements the various wired protocol, such as Ethernet or Token Ring. 
The SNI 108 provides the media dependent physical layer functions such as 
signal encoding, timing generation, and loop-back testing for the various 
wired network protocols, such as Ethernet or Token Ring. Finally, the 
transceiver 108 provides the transmitter and receiver drivers specific to 
the type of physical media for the wired link 22. 
The operation of the base stationary unit 20 and its associated one or more 
wireless terminals 30 operating within its data cell 10 will now be 
explained with reference to FIG. 5. Initially, however, all the wireless 
terminals 30 must complete a registration process to identify themselves 
to the base stationary unit 20a. The registration procedure occurs over 
the air and requires each wireless terminal 30 to know the unique SYNC PN 
sequence used by the base stationary unit 20a. This unique SYNC PN 
sequence will be used in the description set forth hereinafter. The unique 
SYNC PN sequence can be entered manually beforehand in each wireless 
terminal 30. As will be discussed hereinafter, the SYNC PN sequence is 
used to maintain timing of communication between each wireless terminal 
30, which is registered, and the base unit 20, and to decode the status 
signal. Therefore, all registered wireless terminals 30 can communicate 
with the base unit 20. All other wireless terminals 30, although may be 
present in the same communication cell 10, will not be able to communicate 
with the base unit 20. FIG. 5 shows a time scale divided into eight (8) 
periods of time (hereinafter each period is termed a "slot"). A collection 
of contiguous slots will be termed "megaslot". As shown in FIG. 5, an 
example of a megaslot is a collection of seven (7) slots. However, the 
number of slots that comprise a megaslot can vary from time to time. 
However, the maximum size of a megaslot is determined by the frequency 
drift of each of the wireless terminals 30. As will be seen, one of the 
unique features of the method of the present invention, to conserve power 
and bandwidth, is for the stationary base unit 20 to transmit a 
synchronization signal only at the commencement of every megaslot. Since 
frequency drift is the limiting factor for the wireless units 30 to be 
able to lock onto the synchronization signal from the stationary base unit 
20, that becomes the limiting factor as to the maximum size of the 
megaslot. In the preferred embodiment, each slot is on the order of 200 
microseconds in length. The maximum megaslot would be 10 millisec in 
duration, corresponding to a collection of 50 slots. 
Assuming for the moment that initially, only the base stationary unit 20 is 
active. At the commencement of the first slot of the megaslot, the base 
unit transmits a synchronization (SYNC) signal followed by a status 
signal. The status signal can be one of three possibilities: I for Idle 
indicating that no data signal is to follow; R for Reserved indicating 
that what follows immediately would be transmission by one or more of the 
wireless terminals 30; and B for Busy indicating that what follows is data 
transmission from the base unit 20 to one or more of the wireless 
terminals 30. Each of these status signals will be described in greater 
detail hereinafter. 
Assuming that initially, the system is idle then the initial status signal 
that follows the synchronization signal in the first slot transmitted by 
the base unit 20 is an Idle signal. The total amount of time from the 
commencement of the transmission of the SYNC signal to the completion of 
the transmission of the Idle status signal is labeled .tau., and is on the 
order of 50 microsecond. 
The SYNC signal transmitted by the base unit 20 is received by each of the 
wireless terminals 30 within the data cell 10 to the extent that the 
wireless terminal 30 can so receive (the limitation being interference, 
etc.). If the wireless terminal 30 received the SYNC signal, then it is 
used as a clocking signal for the wireless terminal 30. This occurs 
through the action of the sync acquisition unit 74 through the logic 
detect unit 76 to the CLU 72. Furthermore, once the status signal is 
received and is decoded to be Idle by the CLU 72 of each wireless terminal 
30, if the wireless terminal 30 does not request transmission (to be 
discussed hereinafter), then through the circuit shown in FIG. 3, the CLU 
72 would power down the transmitter section and the receiver section of 
the wireless terminal 30, thereby saving power. 
Assuming that the base stationary unit 20 does not have anything to 
transmit. In the method of the present invention, rather than repeating 
the SYNC signal followed by an Idle status signal, the base stationary 
unit 20, if it does not have any data messages to transmit, would defer 
the transmission of SYNC signal accompanied by a status signal until the 
commencement of a subsequent megaslot, i.e. slot number 8. Since each of 
the wireless terminals 30 has received the SYNC signal synchronizing its 
clock signals to that of the stationary base unit 20, the wireless 
terminals will know the beginning of each slot number without having the 
need to actually receive a SYNC signal from the stationary base unit 20. 
Furthermore, each of the wireless terminals would wait a period of .tau. 
from the commencement of the slot, to allow the base unit 20 to transmit 
if the base unit 20 desired to do so. Thereafter, i.e. after the period of 
.tau. from the commencement of the slot, if one of the wireless terminals 
30 desires to transmit, it would transmit a request control signal to the 
base unit 20. Thus, the transmission of the request signal can occur in 
slot number 1 or in a subsequent slot, such as slot number 2. This request 
control signal contains the identity of the wireless terminal 30 that 
desires to transmit subsequently, the identity of the wireless terminal 30 
that should receive the subsequent transmission, the data signal length 
(i.e. number of slots of transmission requested), and for time-based 
service, the request control signal would also contain the frequency of 
the signal. The frequency of the data message times the data message 
length corresponds to the bandwidth requirement of the time-based service. 
If we assume the request signal was transmitted in slot number 2, and if no 
other wireless terminal 30 had attempted to transmit a request control 
signal in slot number 2, then there would be no collision and the base 
unit 20 would receive the request control signal. The base unit 20 would 
respond by transmitting in a subsequent slot, i.e. slot number 3, a SYNC 
signal followed by a Busy status signal. The Busy status signal is then 
followed by a repetition by the data sent by the requesting wireless 
terminal 30, i.e. the wireless terminal 30 that is authorized to transmit, 
the wireless terminal 30 that is authorized to receive, and the length of 
the transmission, and the offset number of slots to the start of 
transmission. 
However, if there is a collision of the request control signal in slot 
number 2, i.e., a plurality of wireless terminals 30 transmit their 
request control signal within time slot number 2, then of course, the base 
stationary unit 20 would not be able to receive the unique request control 
signal and would not be able to honor that request by responding in slot 
number 3 (as explained hereinabove). Thus, there would be no authorization 
by the base stationary unit 20 and the reservation request signal must be 
retransmitted by the wireless terminals 30 requesting authorization for 
subsequent transmission. The retransmission algorithm is a truncated 
binary exponential backoff algorithm. The number of slots before the nth 
retransmission attempt is selected is a uniformly distributed random 
number in the range 0.ltoreq.d&lt;2.sup.k where k is equal to min(n, 10). 
After 15 retransmission attempts, the reservation request process is 
deemed to have failed. This truncated binary exponential algorithm is 
similar to that which is used in Ethernet and provides for stable 
operation in the wireless environment. 
At the start of slot number 3, when the SYNC signal is received by all the 
wireless terminals 30 in the data cell 10 that can receive the SYNC 
signal, the CLU 72 would cause the receiver portion of the wireless 
terminal 30 to be powered on. Once the status signal has been decoded to 
mean "Busy", the CLU 72 continues to maintain power to the receiver 
portion of the wireless terminals 30, for the remainder of the time in the 
slot. This is so that each of the wireless terminals 30 can determine if 
it is the authorized wireless terminal 30 to transmit or is the authorized 
wireless terminal 30 to receive. 
In a subsequent time slot indicated by the offset number, i.e. slot number 
4, the base unit 20 again transmits a SYNC signal at the beginning of the 
slot, followed by a status signal of R for Reserved. Again, since only the 
registered terminals 30 can decode the status signal R, and maintain 
communication timing with the base unit 20, non-registered terminals 30 
will not be able to decode the SYNC or status signals. This then affords a 
limited amount of privacy. 
Once the transmission of the Reserved signal from the stationary base unit 
20 terminates, the wireless terminal 30 authorized to transmit immediately 
begins the transmission of its data signals. This is shown by the time 
delay of .tau. in the time scale shown in FIG. 5 for the wireless terminal 
30 authorized to transmit. The transmission can span over a plurality of 
slots. Each of the wireless terminals 30 turns on its receiver portion at 
the commencement of slot number 4 to receive the SYNC and the status 
signals. Since the status signal is an R, the CLU 72 maintains power to 
the transmitter portion only if the wireless terminal 30 is authorized to 
transmit and the CLU 72 maintains power to the receiver portion only if 
the wireless terminal 30 is authorized to receive. 
Upon termination of transmission by the wireless terminal 30 at the end of 
slot number 6 (shown in FIG. 5), the base stationary unit 20 transmits yet 
another SYNC signal at the commencement of slot number 7. This is followed 
by a yet another status signal of R or reserved. The transmission of the 
SYNC signal and the associated Reserved status signal by the base unit 20 
in slot number 7 serves to signal the wireless terminal 30 authorized to 
receive to transmit a response signal. If the authorized wireless terminal 
30 received the transmitted signal, then it would transmit a response 
signal. This would be received by the base stationary unit 20 and would 
end the transmission of one wireless terminal 30 to another. 
On the other hand, if no response signal is received by the base stationary 
unit 20, then the base stationary unit 20 in a subsequent time slot would 
relay the data message signal transmitted by the authorized wireless 
terminal 30 in time slots 4, 5 and 6. The base stationary unit 20 can 
relay this data message signal in one of two ways. If it is determined 
that the wireless terminal 30 authorized to receive is still in the data 
cell 10, but is out of the range of the wireless terminal 30 which is 
authorized to transmit, then the base stationary unit 20 in the data cell 
10 would transmit "over the air" within the data cell 10 to the wireless 
terminal 30 which is authorized to receive. On the other hand, if it is 
known that the wireless terminal 30 authorized to receive has moved into a 
different data cell, e.g. data cell 10b, and has registered with the base 
stationary unit 20b in that data cell 10b, then the base stationary unit 
20a would transmit over the wired connection 22 to the second base 
stationary unit 20b for retransmission, "over the air" within the second 
data cell 10b. 
For time-based services, e.g. voice, the operation is exactly the same to 
account for out-of-range destinations. However, this is done only for the 
first data message signal in the time-based service data stream. If the 
wireless terminal 30 authorized to receive is in the range, and responds 
with a response signal, then the response signal is not transmitted for 
subsequent data message signals to save bandwidth. If the wireless 
terminal 30 authorized to receive moves out-of-range, as indicated by, for 
example, a drop in the signal-to-noise ratio received by the wireless 
terminal 30, then the wireless terminal 30 authorized to receive transmits 
a relay request signal to the base stationary unit 20 during an idle time 
slot. The relay request signal informs the base unit 20 that the wireless 
terminal 30 authorized to receive cannot receive the data signal directly 
from the transmitting wireless terminal 30 and requests the base unit 20 
to relay or retransmit the data signal. The base stationary unit 20 
responds with a relay confirmation message signal to the wireless terminal 
30 which is authorized to receive. The relay confirmation signal indicates 
the offset in terms of number of time slots for the relayed transmission. 
The wireless terminal 30 authorized to receive continues to monitor the 
time slots assigned to it for direct transmission. However, if the 
wireless terminal 30 authorized to receive moves in the range as indicated 
by an increase in the signal-to-noise ratio received by it, for direct 
transmission, the wireless terminal 30 authorized to receive would 
transmit a direct request message to the base stationary unit 20 during an 
idle time slot. The base stationary unit 20 would then respond with a 
direct confirmation message signal to the wireless terminal 30 authorized 
to receive to cease the relaying of the data message signals. 
From the foregoing, it can be seen that there are a number of advantages of 
the system of transmission of the present invention. 
First, in the wireless method and system of the present invention, both 
asynchronous and time-based services or synchronous transmissions can be 
accomplished. The system is based on channel reservation requests by 
active wireless terminals with contention resolution and authorization by 
the base stationary unit. The data message signals transmitted by the 
authorized wireless terminal can be either immediately for asynchronous 
service or periodically for time-based service. In the event of collision 
in the request by a plurality of wireless terminals for reservation of 
channel, reservation request collisions are detected in one time slot. For 
an idle channel, access latency is at most two time slots for the request 
signal by the wireless terminal to the base stationary unit and the 
authorization signal from the base unit back to the requesting wireless 
terminal. This provides low access delay under idle conditions. In 
addition, there is no segmentation of data messages thereby saving channel 
and processing overhead. Segmentation is the division of the message 
signal into slot-size segments, each separated by .tau. time period. In 
the method and apparatus of the present invention the message signal is 
transmitted continuously without any segmentation. 
If the wireless terminal authorized to receive is in the same data cell, 
and it correctly receives the data message signals, the wireless terminal 
authorized to receive sends a response message to the base stationary unit 
confirming receipt of the data message signal. Otherwise, the base 
stationary unit relays the data message signal. Therefore, the base 
stationary relays data message signals only for out-of-range wireless 
terminals. For time-based services, the control overhead for relaying 
messages is only incurred at the transitions when the wireless terminal 
authorized to receive moves in and out of range. Except for the control 
overhead, recovery from transmission bit errors is done by the Logical 
link Control (LLC) or upper layers, if necessary. A wireless terminal 30 
may receive a message that has a random bit error that the FEC decoder 68 
cannot correct. The higher layer protocols will recover the message by 
retransmitting. The PCU 80 is not involved in the retransmission. 
The base stationary unit 20 can authorize itself for message transmission 
when it receives a data message from a second base stationary unit 20 over 
a wired connection 22 or if it must relay a data message signal to an 
out-of-range wireless terminal 30 authorized to receive or it must relay a 
broadcast message to all the wireless terminals 30 in the data cell 10. 
When a wireless terminal 30 authorized to transmit desires to transmit a 
broadcast message, none of the wireless terminals in that data cell 10 is 
authorized to receive during the transmission by the wireless terminal 30 
authorized to transmit. The wireless terminals 30 in that data cell 10 
receive the broadcast message only as broadcasted by the base stationary 
unit 20 to prevent receipt of duplicate messages. Lastly, with the CLU 72 
controlling the power to the wireless terminal 30 dependent upon the 
status signal, considerable power savings can be achieved. 
It should be noted that the reference in the claims set forth hereinafter 
to a "first slot", or a "second slot", etc. do not refer to the timing of 
the slot number. Rather the reference to "first", or "second" etc., is 
merely to distinguish one slot from another. In addition, while the method 
and the apparatus has been described with respect to a Pseudo Code Noise 
system or CDMA, clearly it can be used in FDMA, or any other form of 
wireless technology or medium.