Abstract:
Disclosed is an apparatus for encoding a plurality of data streams in a code division multiple access format to produce a composite signal. The apparatus comprises a plurality of channel units coupled in series, where each channel unit encodes at least one of the plurality of data streams. Each channel unit also combines the data encoded therein with a preceding encoded output signal provided by a preceding one of the channel units to thereby produce an associated encoded output signal. At least one channel unit is capable of providing the associated encoded output signal as a direct output signal to a first subsequent channel unit, and of providing a bypass output signal having cumulative encoded data to a further subsequent channel unit to effect a bypass of the first subsequent channel unit.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to code division multiple access (CDMA) wireless telecommunications, and more particularly, to automatic data bypass of a failed or removed code division multiple access channel unit. 
     BACKGROUND OF THE INVENTION 
     In wireless telecommunication systems employing code division multiple access, each user is assigned a different coding scheme to code individual data bits to be transmitted, such as the data bits of digitized voice signals. These coding schemes are orthogonal or partially correlated to each other, such that it is possible to identify the user based on an analysis of the codes used in the transmission. Consequently, more than one user can communicate on the same frequency channel. 
     FIG. 1 schematically illustrates base station transmitter electronics of a prior art code division multiple access system. Input information-bearing signals such as analog voice of a plurality of communication sessions are received from the telephone network by controller 110. The input signals are converted by controller 110 to baseband data streams d 1  -d N , each of which contain data bits of one or more of the input signals. Code division multiple access channel units 102 l  -102 N , coupled in series, each include an associated code division multiple access chip encoder 104 l  -104 N , which encodes the corresponding data stream d 1  -d N  and supplies an encoded output to a corresponding digital combiner 106 l  -106 N . Each combiner 106 i  adds the encoded signal from the associated chip encoder with an output encoded signal cd i-1  from the previous channel unit 102 i-1 . Thus, the digital combiners add the encoded signals progressively. Hence, encoded signal cd 1  includes only data stream d 1  (encoded), while encoded signal cd N  includes all data streams d 1  -d N  (encoded). 
     Accordingly, the circuit arrangement of FIG. 1 can be referred to as a &#34;daisy-chain&#34; arrangement. Each channel unit 102 i  has a fixed, predetermined delay so that all the encoded data is substantially synchronized when combined to form composite signal cd N . The composite signal cd N  is then applied to analog conversion unit (ACU) 130, to CDMA radio 140 and antenna AT, where it is transmitted to a plurality of wireless communication terminals, e.g., cellular telephones. 
     A drawback of the above-described daisy-chain arrangement is that if one of channel units 102 l  -102 N  should fail, all the encoded data from the previous units would be lost. For example, if unit 102 3  fails, the data from units 102 1  -102 2  will be lost. 
     Moreover, it would be desirable to have the capability or removing any of the units 102 i  for maintenance or otherwise without losing encoded data from the other units. 
     Accordingly, there exists a need for a system without this &#34;single point of failure&#34; deficiency, which can maintain synchronization of the data within output composite signal cd N  when one or more of the channel units either fail or are removed. 
     SUMMARY OF THE INVENTION 
     In an illustrative embodiment of the present invention, disclosed is an apparatus for encoding a plurality of data streams in a code division multiple access format to produce a composite signal. The apparatus comprises a plurality of channel units coupled in series, where each channel unit encodes at least one of the plurality of data streams. Each channel unit also combines the data encoded therein with a preceding encoded output signal provided by a preceding one of the channel units to thereby produce an associated encoded output signal. At least one channel unit is capable of providing the associated encoded output signal as a direct output signal to a first subsequent channel unit, and of providing a bypass output signal having cumulative encoded data to a further subsequent channel unit in order to bypass the first subsequent channel unit, such as when it is malfunctioning or electrically disconnected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, reference is had to exemplary embodiments thereof, considered in conjunction with the accompanying drawings in which like reference numerals depict similar or identical elements, wherein: 
     FIG. 1 is a block diagram of prior art code division multiple access transmitter electronics; 
     FIG. 2 is a block diagram of code division multiple access transmitter electronics in accordance with the present invention; 
     FIG. 3 illustrates exemplary control signal flow between channel units; 
     FIG. 4 is a schematic block diagram of an illustrative channel unit in accordance with the present invention; 
     FIG. 5 illustrates exemplary cumulative data delays in channel units; 
     FIG. 6 is a schematic diagram of an illustrative logic control circuit; 
     FIG. 7 is a block diagram of an exemplary analog conversion unit; 
     FIG. 8 is a block diagram of an alternative embodiment of the present invention; and, 
     FIG. 9 illustrates a block diagram of an alternative exemplary channel unit. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For purposes of illustration, exemplary embodiments of the invention will be presented below as forming a portion of a base station transmitter in a wireless telecommunication system. It is understood, however, that these embodiments are presented for illustrative purposes only, and that the invention may also be implemented in other systems, such as in time division multiple access (TDMA) systems. 
     FIG. 2 is a block diagram of a first embodiment of code division multiple access transmitter electronics in accordance with the present invention, designated generally as 200. Input information-bearing signals from the telephone network are received by controller 210 and converted to digital data streams d 1  -d N  on respective lines 207 l  -207 N . Each data stream d i  typically includes a plurality of information-bearing signals of different communication sessions. Data streams d 1  -d N  are applied to channel units 202 l  -202 N , respectively, where the individual data bits of the data streams are encoded in a code division multiple access format. The channel units are typically integrated circuit cards that can be easily removed from the system for maintenance or replacement. Channel units 202 l  -202 N  comprise a channel unit &#34;cluster&#34;. Additional clusters can be also provided, each of which supplies a composite encoded output signal as cd N  to analog conversion unit 230. 
     In this embodiment, each channel unit 202 i  can provide a direct output signal cd i  on output port 215 i  and a bypass output signal bd i  on bypass line 227 i . Direct output signal c i  is an encoded data signal similar to signals cd 1  -cd N  of the prior art system of FIG. 1. Thus, if all channel units 202 l  -202 N  are operating properly, signal cd 1  will contain encoded data of data streams d 1 , signal cd N  will contain encoded data of data streams d 1  -d N , and so on. In this scenario, no bypass signals bd 1  bd N  will be provided. It is noted that at any given time during system operation, some of the communication channels may not be used. In this case, one or more of the channel units may have no incident data stream d i  applied. At such time, each of these channel units will not encode any data, but will just operate to pass the cumulative encoded data applied to its input port 213 i  to the next functional channel unit. 
     When any channel unit 202 i  is either malfunctioning, becomes electrically disconnected, or is to be physically removed for maintenance or otherwise, the immediately preceding channel unit 202 i-1  in the chain is apprised of this condition (e.g., by a command from another channel unit or from controller 210) and responds by providing bypass signal bd i-1  to the subsequent adjacent channel unit 202 i+1 . Concurrently, a command originating either from channel unit 202 i+1  or from controller 210 is sent to channel unit 202 i , causing direct output signal cd i  to be suspended. Bypass output signals bd 1  -bd N-2  are time delayed versions of direct output signals cd 1  -cd N-2 , respectively. Each time delay corresponds to the delay that each channel unit normally incurs from input port 213 i  to output port 215 i  . Bypass signal bd i-1  is provided via bypass line 227 i-1  to input port 213 i+1  of channel unit 202 i+1  , since bypass line 227 i-1  connects to a common bus line also used for signal cd i  (when not suspended). Hence, the encoded output data from unit 202 i-1  bypasses the malfunctioning or removed channel unit 202 i , whereby encoded data from the channel units preceding the malfunctioning channel unit are not lost. Synchronization of the encoded data is maintained by virtue of the time delays incorporated within the bypass signals. Clock pulses and control signals are provided by controller 210 on lines CCL to each channel unit 202 l  -202 N  to facilitate the synchronization of the data. 
     Analog conversion unit 230 receives, at input port 213 a , either direct signal cd N  from the last channel trait 202 N  in the chain or bypass signal bd N-1  from the next to last channel unit 202 N-1  (not shown). ACU 230 converts the encoded data applied thereto to analog form and supplies an analog output to a CDMA radio for subsequent wireless transmission to wireless communication terminals. 
     FIG. 3 illustrates three consecutive channel units 202 i-1 , 202 i  and 202 i+1  and a preferred control signal arrangement to effect bypass of a selected channel unit. Each channel unit such as 202 i  provides a control signal EN i  on associated control line CL i . Control line CL i  is split into control line DL i-1  supplied to channel unit 202 i-1  and control line BL i-2  supplied to channel unit 202 i-2 , where each of these control lines carry the EN i  signal. The logic state of control signal EN i  will determine whether a bypass is implemented. 
     By way of example, when the three channel units of FIG. 3 are functioning properly, channel unit 202 i+1  supplies signal EN i+1  on line DL i  at a first logic state causing signal cd i  to be outputted. Signal EN i+1  is also provided on line BL i-1  at the same logic state, which disables the outputting of bypass signal bd i-1 . Hence, the signal applied to channel unit 202 i+1  on port 213 i+1  is cd i  in this case. If, however, channel unit 202 i  is providing defective data or otherwise malfunctioning, this condition is detected by channel unit 202 i+1  , which responds by changing the logic state of control signal EN i+1  to a second logic state. This results in suspending direct output signal cd i  and causing bypass signal bd i-1  to be outputted. Only bypass signal bd i-1  is thereby applied to port 213 i+1  in this scenario, and the encoded data from the channel units preceding channel unit 202 i  are not lost. Since control lines DL i  and BL -1  are derived from a common control line, either signal cd i  or bd i-1 , but not both, will appear at port 213 i+1  at any given time. 
     Each channel unit such as 202 i  also supplies a ground potential SG i  on port 338 i , which is coupled to port 329 i+1  of the subsequent channel unit 202 i+1 . When channel unit 202 i  is removed for maintenance or otherwise, the connection between these ports is broken, forcing signal EN i  to the second logic state, whereby channel unit 202 i  is bypassed. 
     Optionally, controller 210 can provide, via lines CCL, (see FIG. 2) additional control signals to those generated by the neighboring channel units to effect bypassing of defective or removed channel units. In the alternative, each channel unit would report defects in data received from the previous neighbor and only controller 210 would provide the control signals to implement a bypass. 
     Referring to FIG. 4, a block diagram of an exemplary channel unit 202 i  is shown. In this example, input data streams d i  are comprised of a pair of data streams d ia  and d ib , each carrying data of a separate communication session. Channel unit 202 i  employs a pair of code division multiple access chip encoders 412 i  -a and 412 i  -b to encode the respective data streams d ia  and d ib . In the general case, the number of chip encoders employed within each channel unit corresponds to the number of input data streams to be encoded by that channel unit which is two in the current example. Code division multiple access chip encoders are known in the art and are available commercially as Application Specific Integrated Circuits (ASICs) from QUALCOMM Corporation located in San Diego, Calif., and from other manufacturers. Each chip encoder 412 i  -a and 412 i  -b is programmed to compensate for cumulative delays of data through the channel units during normal operation (with or without bypass signals being selected), thereby enabling synchronization of the encoded data outputs of each channel unit 202 i . Clock pulses are supplied to the chip encoders on lines CCL i  to provide a common time reference and facilitate synchronization. 
     FIG. 5 illustrates cumulative delays through code division multiple access channel units (CCU) 202 l  -202 N  that are compensated for by the programming of chip encoders 412. Each CCU is assumed in this example to delay the encoded input data from the preceding CCU by four clock cycles. As such, the encoded data streams d 1  of signal cd 1  are delayed within CCU 202 2  by four clock cycles and by another four clock cycles within CCU 202 3 , and so forth. After being combined to form composite signal cd N , the data streams cd 1  will have been delayed by 4×(N-1) clock cycles. At the other extreme, the data streams d N  encoded by CCU 202 N  do not incur any delay after being combined with data streams cd N-1  to form composite signal cd N . As such, chip encoders 412 N  -a and 412 N  -b within CCU 202 N  are programmed to delay the input data stream d N  by 4×(N-1) clock cycles; chip encoders 412 1  -a and 412 1  -b are programmed to delay the input data streams d 1  by zero clock cycles, and so on, such that all encoded data is combined in synchronism to form composite signal cd N . Additional delays are incurred when bypass paths are selected in order to maintain data synchronization, as will be described below. 
     With continuing reference to FIG. 4, digital combiner 406 i  is coupled to each chip encoder and to input port 213 i , and receives the encoded data streams from the chip encoders and encoded data stream cd i-1  or bd i-2  incident upon input port 213 i  . Digital combiners are known in the art and can be incorporated within a field programmable gate array (FPGA), here FPGA 460 i . Digital combiner 406 i  combines the encoded data streams it receives to form a composite output signal S Ci . This signal is routed in either a bypass path defined by delay element 430 i  and bypass buffer 410 i  to produce bypass signal bd i , or in a direct path encompassing direct buffer 420 i  to produce direct output signal cd i . Direct buffer 420 i  can be a tristate logic buffer controlled (i.e., &#34;enabled&#34;) by signal EN i+1  originating from neighboring channel unit 202 i+1  . Bypass buffer 410 i  can also be a tristate buffer, enabled by control signal EN i+2  originating from channel unit 202 i+2  and inverted by invertor 440 i . 
     As explained above in reference to FIG. 3, when channel unit 202 i  is functioning properly, the subsequent channel unit 202 i+1  provides signal EN i+1  at a first logic state, e.g., LOW, thereby allowing data to pass through direct buffer 420 i  such that signal cd i  is outputted. Concomitantly, bypass buffer 410 i-1  (not shown) of the preceding channel unit 202 i  -1 is disabled, thus suspending bypass signal bd i-1  so that only signal cd i  is applied to channel unit 202 i+1 . When channel unit 220 i  is malfunctioning or electrically disconnected, EN i+1  is HIGH and the opposite occurs. When channel unit 220 i+1  is malfunctioning or disconnected, control signal EN i+2  supplied from channel unit 202 i+2  is HIGH, causing bypass buffer 410 i  to output bypass signal bd i , which is supplied to channel unit 202 i+2 . 
     In the bypass path, the delay introduced by delay element 430 i  is equivalent to the delay normally incurred from input port 213 i  through digital combiner 406 i  to direct output port 215 i  , excluding the delay through direct buffer 420 i . Delay element 430 i  receives clock pulses and control bits from controller 210 via lines CCL i  to insure that the proper delay is introduced, e.g., a predetermined number of clock pulses. Accordingly, when the bypass path is selected, the output data can arrive at channel unit 202 i+2  with the same phase as in the normal operation case--i.e., the phase of the direct output signal cd i  as delayed through channel unit 202 i+1 . Thus, synchronism of the data is maintained. For instance, in the example presented in FIG. 5 where each channel unit normally incurs a four clock cycle delay, the delay introduced by delay element 430 i  would be four clock cycles. 
     The data stream input on port 213 i  from the previous neighbor 202 i-1 , i.e., direct signal cd i-1  or bypass signal bd i-2 , is sampled by detection circuit 470 i , also included within FPGA 460 i . When detection circuit 470 i  detects properly formatted data within the input data stream, e.g., by detecting correct parity bits, it provides signal D ERRi  on line 475 i  at a first logic state, e.g., HIGH. When faulty data is detected, such as when there is a parity bit error, signal D ERRi  is provided at the opposite logic state, e.g., LOW. Logic control circuit 480 i  receives signal D ERRi  and provides signal EN i  as HIGH if signal D ERRi  is indicative of faulty data. Logic control circuit will also provide signal EN i  as HIGH if voltage potential SG i-1  indicates that the ground connection between port 329 i  and port 338 i  is broken. Signal EN i  will also be HIGH if the logic control circuit receives a specific command from controller 210 on one of lines CCL i . 
     FIG. 6 is a schematic diagram of an exemplary logic control circuit 480 i  which can be utilized within an associated channel unit 202 i . If any of three input logic signals D ERRi , BT i  or SG i-1  applied to OR gate 610 i  are HIGH, then output signal EN i  is HIGH, thereby effecting a bypass of the previous channel unit 202 i-1 . Logic signal BT i  is provided by register 620 i , and is HIGH if control bits on line CCL i  originating from controller 210 indicate that a bypass of the previous channel unit 202 i-1  should be implemented. For instance, an operator wishing to perform maintenance on the previous channel unit 202 i-1  can enter a specific command on controller 210 to cause that channel unit to be bypassed prior to the operator physically removing it. During normal operation, logic signal SG i-1  is pulled LOW by the ground connection in unit 202 i-1  but floats HIGH if the ground connection is broken. Signal D ERRi  is HIGH when faulty data is detected, as discussed above. 
     FIG. 7 shows a block diagram of an exemplary analog conversion unit (ACU) 230a. Encoded output signal cd N  from channel unit 202 N  or bypass output signal bd N-1  from channel unit 202 N-1  is applied to input port 213 a . Detection circuit 470 a  detects whether data within signal cd N  is faulty and outputs logic signal D ERRa  on line 475 a  indicative of this determination. Logic control circuit 480 a  provides control signal EN a  at a logic level responsive to signals D ERRa  and SG N  from channel unit 202 N  and also to control bits from the controller 210 on lines CCL a . Thus, when any of these signals indicate that a bypass of the last channel unit 202 N  should be implemented, signal EN a  is provided as a logic HIGH, which causes the corresponding buffers within channel units 202 N  and 202 N-1  to effect a bypass. The resulting encoded input signal to the ACU--i.e., signal cd N  or bd N-1  --is applied to D/A converter 720 where it is converted to analog form and outputted to the CDMA radio. Optionally, additional encoded input signals from other clusters are applied to ACU 230 a  on bus lines 710. These encoded signals are converted to analog as well, and then outputted. The additional encoded signals can also be detected for faulty data by employing a detection circuit 470 i  and logic control circuit 480 i  for each cluster input. Each logic control circuit would then supply the last and next to last channel units of the associated cluster with a control signal EN i  to control bypass of the last channel unit in that cluster. 
     FIG. 8 schematically illustrates an alternate embodiment of code division multiple access transmitter electronics in accordance with the present invention, designated generally as 800. Controller 210 provides data streams d 1  -d N  on respective lines 207 l  -207 N  as in the embodiment of FIG. 1. Code division multiple access channel units 802 l  -802 N-1  differ from the above described channel units in that each channel unit 802 i  always provides, when functioning properly, both a direct encoded output signal cd i  &#39; and a bypass encoded output signal bd i  &#39; simultaneously, each having cumulative encoded data. The cumulative encoded data includes data encoded in that channel unit 802 i  containing data stream d i  (encoded) combined with data encoded in the preceding channel units 802 l  -802 i-1  when each channel unit is operational. Each bypass output signal bd i  &#39; is substantially the same as the direct output signal cd i  &#39; except delayed by a predetermined delay, corresponding to the delay of encoded data through a channel unit, in order to maintain synchronization of the cumulative encoded data. Each channel unit 802 i  (excluding channel units 802 1  and 802 2 ) receives signals cd i-1  and bd i-2  on respective input ports 213 i  and 819 i  and selects which encoded output signal--whether cd i-1  or bd i-2  --is to be combined with the encoded data stream d i  within that unit. Encoded data signals cd N  &#39; and bd N-1  &#39; are applied to analog conversion unit 830, which analogously selects which of these signals is to be converted to analog form and outputted to the CDMA radio. 
     FIG. 9 is a block diagram of an exemplary channel unit 802 i , which can be used for any of channel units 802 l  -802 N . Encoded input signal cd i-1  &#39; is received at port 213 i  and applied to both detection circuit 470 i  and to an input port of single pole two throw (SP2T) switch 912 i  via line 921 i . Detection circuit 470 i  provides logic level output signal D ERRi  on line 475 i  as described above, which is HIGH when faulty data is detected. In this embodiment, signal D ERRi , is applied via line 914 i  to a control port of switch 912 i  to control its switch position. Bypass input signal bd i-2  &#39; is applied to input port 819 i  and routed to the other switch input port of switch 912 i  via line 923 i . Hence, when signal D ERRi  is HIGH, bypass input signal bd i-2  &#39; is switched to digital combiner 406 i  ; when D ERRi  is LOW indicating proper data without faults, then direct signal cd i-1  &#39; is switched to the digital combiner. Signal D ERRi  is also provided to the controller to apprise it of data faults detected. Combined signal Sc i  is outputted by digital combiner 406 i , delayed by delay circuit 430 i  in the bypass path to produce bypass signal bd i  &#39;. Signal Sc i  is directly outputted in the direct path to produce signal cd i  &#39;. The delay circuit, detection circuit, SP2T switch and digital combiner are typically incorporated within a field programmable gate array, here FPGA 960 i . It is noted that while the buffers have been removed in the output paths, they can optionally be included to suspend the encoded output signals responsive to commands from controller 210 or from other channel units. Switch 912 i  can also be modified to be responsive to commands from controller 210 and/or from other channel units. 
     It will be understood that the embodiments disclosed herein are merely exemplary and that one skilled in the art can make many modifications and variations to the disclosed embodiments without departing from the spirit and scope of the invention. For example, while the above embodiments have been disclosed as having bypass lines that each bypass a single channel unit, it is understood that analogous embodiments can be constructed having the capability of bypassing two or more consecutive channel units. Moreover, while the disclosed embodiments have described in relation to a code division multiple access system, the invention may also be applicable to TDMA systems. Accordingly, all such modifications and variations are intended to be included within the scope of the invention.