Apparatus, and associated method, for transmitting and receiving a multi-stage, encoded and interleaved digital communication signal

Apparatus and associated method for improving the radio link performance of a radio communication system, such as a cellular communication system. Multi-stage encoding and interleaving of the data bits of a digital information signal is performed at a single logical device, such as a radio base station. By performing two stages of interleaving over the same number of information frames of the data bits, only a single buffering stage is required to perform such multi-stage interleaving.

The present invention relates generally to the transmission of a digital 
communication signal on a communication channel, such as a communication 
channel forming a link between a radio base station and a mobile terminal 
of a cellular communication system. More particularly, the present 
invention relates to transmitter apparatus, and an associated method, for 
forming a multi-stage, interleaved and encoded communication signal and to 
receiver apparatus, and an associated method, for deinterleaving and 
decoding a multi-stage interleaved and encoded communication signal. 
Improved radio link performance is provided to overcome, e.g., distortion 
of the communication signal caused by fading and other distortion during 
transmission of the signal upon the communication channel. The 
informational content of the communication signal can be recreated with a 
bit error rate of less than 10.sup.-6 without introducing significant 
amounts of signal transmission delay. 
When embodied in a cellular communication system in which communication 
signals are transmitted upon channels susceptible to multi-path fading, 
improved radio link performance is provided without an increase in the 
transmission delay otherwise required to provide multi-stage encoding and 
interleaving. The multi-stage encoding and interleaving can be performed 
at a single logical device, such as at a radio base station of the 
cellular communication system. 
BACKGROUND OF THE INVENTION 
Communication systems are increasingly constructed to permit the 
utilization of digital communication techniques by which to communicate 
information between a sending station and a receiving station. In a radio 
communication system, the communication channel is formed of a portion of 
the electromagnetic spectrum, i.e., the "bandwidth" allocated to the 
communication system. 
A cellular communication system is a type of radio communication system and 
is exemplary of a type of communication system which is increasingly 
constructed to utilize digital communication techniques. 
By utilizing a digital communication technique, the information of a 
communication signal can typically be more efficiently communicated 
between the sending station and the receiving station. In a radio 
communication system, the bandwidth allocated to the radio communication 
system is typically limited. The improved efficiency provided by the 
utilization of a digital communication technique permits the allocated 
bandwidth to be utilized more efficiently. By utilizing a digital 
communication technique, the communication capacity of such a radio 
communication system can sometimes be increased. In radio communication 
systems, the communication capacity of the system is limited by the 
allocated bandwidth. In a multi-user, radio communication system, for 
instance, an increase in the communication capacity permits additional 
users to communicate by way of the communication system. 
A radio frequency link forming a communication channel between a sending 
station and a receiving station of a radio communication system is 
typically not an ideal, loss-free communication channel. A communication 
signal might be susceptible to degradation caused by multi-path fading. If 
significant, such fading might prevent the accurate recovery at the 
receiving station of the informational content of at least the portions of 
the communication signal subjected to such fading. 
To increase the probability that the informational content of a digital 
communication signal transmitted by the sending station can be recovered 
once received at the receiving station, the data bits which are modulated 
to form the communication signal are sometimes encoded according to an 
encoding technique. Coding of the signal increases the redundancy of the 
signal. Even if portions of the communication signal are so distorted as 
to prevent some of the data bits modulated thereon to be recovered, the 
increased redundancy introduced by encoding the data bits increases the 
probability that the informational content of the signal can be recreated 
at the receiving station. 
Various block and convolutional coding techniques have been developed to 
increase the redundancy of the signal at a sending station. Corresponding 
block and convolutional decoding techniques have similarly been developed 
to decode the communication signal, once received at the receiving 
station. 
In at least one type of block coding technique, check bits are concatenated 
to blocks of data bits of which the communication signal is to be formed. 
The check bits are of values dependent upon the values of the data bits of 
such blocks of data. 
In at least one type of convolutional coding technique, a coded sequence is 
formed of the data bits. The values of the bits of the coded sequence are 
dependent upon not only the bit values of the data bits which are to be 
encoded but also upon bit values of preceding bit sequences of data bits 
previously encoded. 
Encoding of the data bits which are modulated to form a communication 
signal advantageously facilitates the recreation of the informational 
content of the signal when the interference introduced upon the signal is 
of short duration. If, however, the interference introduced upon the 
communication signal is of a lengthier duration, e.g., greater than 
several bits, encoding of the data bits does not ensure that the 
informational content of the signal shall be able to be accurately 
recreated. 
Various interleaving techniques have been developed to reduce the 
possibility that interference introduced upon a communication signal 
during its transmission upon a communication channel shall prevent the 
recovery of the informational content thereof. 
When the data bits are interleaved, consecutive data bits of the 
communication signal are "spread-out" so as not to be transmitted 
consecutively. Once the communication signal is received at the receiving 
station, the data bits are recombined. Because the data bits are 
spread-out over time, distortion is less likely to distort the consecutive 
bits in a manner to prevent the recreation of their informational content, 
once received at the receiving station. 
Digital communication techniques are utilized in various cellular 
communication systems. For instance, a cellular communication system 
constructed pursuant to the standard specification of the Global System 
for Mobile communications (GSM) utilizes a digital communication 
technique. And, a cellular communication system constructed according to 
the EIA/TIA IS-95 specification, a CDMA (Code Division Multiple Access) 
system similarly utilizes digital communication technique. Prior to 
transmission of communication signals generated during operation of such 
systems, the data bits, of which the communication signals are formed, are 
encoded and interleaved. In a CDMA-based system, modulation is typically 
preceded by spreading of the coded and interleaved bits by a code 
sequence. Corresponding despreading is performed at a receiver. 
Operational protocols for the encoding and interleaving of data bits are 
also set forth in the respective standard specifications. Corresponding 
decoding and deinterleaving protocols are also set forth. 
Although encoding and interleaving of the data bits of a communication 
signal increase the possibility that the informational content of the 
communication signal, subjected to interference during its transmission 
upon the communication channel, can be recreated, such encoding and 
interleaving, causes signal transmission delay. Interference may be 
caused, e.g., by distortion due to noise and both adjacent- and co-channel 
interference. In a CDMA-based system, interference can be caused from 
other users. The corresponding decoding and deinterleaving, causes 
additional signal transmission delay. If extensive, the transmission delay 
can also interfere with the quality of communications between a sending 
station and a receiving station. 
When the radio communication system is utilized to transmit data rather 
than speech information, radio link performance is of increased 
significance. For instance, a bit error rate of 10.sup.31 3 is normally 
acceptable when the communication signal is formed of speech information. 
However, when data forms the informational content of the communication 
signal, a bit error rate performance of better than 10.sup.-6 is instead 
sometimes required. 
Such a level of radio link performance requires additional encoding and 
interleaving of the data bits of a communication signal to be transmitted. 
However, if there is a correspondent increase in the signal transmission 
delay caused as a result of the additional encoding and interleaving, the 
resultant signal delay might be unacceptably large. 
Utilization of a multi-stage encoding and interleaving technique permits 
the radio link performance to be improved. However, conventional 
multi-stage encoding and interleaving techniques typically introduce 
unacceptably large signal transmission delay. 
A manner by which the radio link performance can be improved without 
causing a corresponding increase in the transmission delay would be 
advantageous. 
It is in light of this background information relating to digital 
communication techniques that the significant improvements of the present 
invention have evolved. 
SUMMARY OF THE INVENTION 
The present invention advantageously provides transmitter apparatus, and an 
associated method, for forming a multi-stage interleaved and encoded 
communication signal. The present invention further advantageously 
provides receiver apparatus, and an associated method, for deinterleaving 
and decoding the multi-stage interleaved and encoded communication signal. 
The multi-stage interleaving and encoding of a communication signal 
facilitates recovery of the informational content of the signal subsequent 
to its transmission upon a communication channel susceptible to 
interference, such as a communication channel susceptible to multi-path 
fading. 
Improved radio link performance is provided to overcome distortion of the 
communication signal caused by such multi-path fading during transmission 
of the signal upon the communication channel. 
In one aspect of the present invention, transmitter apparatus forms a 
multi-stage encoded and interleaved signal. Outer, block encoding is 
performed across a selected number of frames of information, i.e., "data", 
bits which form a communication signal to be transmitted upon a 
communication channel. An outer interleaver interleaves groups of bits 
across the selected number of frames. An inner encoder convolutionally 
encodes bits of each of the frames of data bits. And, an inner interleaver 
interleaves bits across the selected number of frames. 
In an another aspect of the present invention, receiver apparatus decodes 
and deinterleaves a communication signal formed of a multi-stage, encoded 
and interleaved set of frames of data bits received thereat. An inner 
deinterleaver deinterleaves at least selected bits across a selected 
number of the successive frames of the bits. An inner decoder 
convolutionally decodes bits of each of the frames of the selected number 
of the successive frames. An outer deinterleaver deinterleaves groups of 
bits across the selected number of frames of the bits. And, an outer block 
decoder decodes blocks of the bits across the selected number of the 
successive frames of the bits. 
Because the outer and inner interleaver interleave groups of data bits and 
individual ones of the data bits, respectively, across the same number of 
selected frames, only a single buffering stage is required to buffer the 
selected number of frames to permit the respective interleaving operations 
to be performed. 
Analogously, because the inner deinterleaver and outer deinterleaver 
deinterleave data bits and groups of data bits, respectively, across the 
same number of frames, only a single buffer is required to buffer the 
signal to permit both deinterleaving operations to be performed. 
Because only a single buffering stage is required by the transmitter 
apparatus to form the multi-stage interleaved and encoded signal, and only 
a single buffering stage is required by the receiver apparatus, a 
substantial reduction in the signal transmission delay is possible. 
In another aspect of the present invention, apparatus positioned at a radio 
base station operable in a cellular communication system forms a 
multi-stage encoded and interleaved signal for communication upon a 
communication channel susceptible at least to multi-path fading. Outer 
interleaving and encoding is performed across a selected number of frames 
of the bits into which a sequence of data bits is formatted. An inner 
encoder encodes data bits of each of the frames of the selected number of 
frames. And, an inner interleaver interleaves data bits across the 
selected number of frames. Modulation apparatus thereafter modulates the 
multi-stage--encoded and interleaved frames of bits. And, the resultant 
signal is transmitted to a remotely-positioned mobile terminal. 
The radio base station further includes analogous multi-stage decoding and 
deinterleaving apparatus for decoding and deinterleaving a multi-stage 
encoded and interleaved signal transmitted thereto. A buffer buffers a 
selected number of frames of the signal received at the radio base 
station. An inner deinterleaver deinterleaves data bits of the selected 
number of frames buffered by the buffer. An inner decoder decodes data 
bits of each of the selected number of frames buffered by the buffer. An 
outer deinterleaver deinterleaves groups of data bits across the frames 
buffered by the buffer. And, an outer decoder block decodes groups of data 
bits across the frames buffered by the buffer. 
When embodied in a cellular communication system, a mobile terminal is 
constructed to include apparatus analogous to the apparatus forming 
portions of a radio base station to deinterleave and decode signals 
transmitted thereto by a radio base station. The mobile terminal is 
similarly also constructed to include apparatus to encode and interleave 
signals to be communicated to the radio base station. 
In these and other aspects, therefore, apparatus encodes and interleaves 
data bits formatted into frames to form a communication signal which is to 
be transmitted upon a communication channel from a communication station 
to a remote device. An outer encoder is coupled to be provided with the 
data bits. The outer encoder encodes at least selected data bits across a 
selected number of the frames of the data bits. An outer interleaver is 
coupled to be provided with the communication signal, once encoded by the 
outer encoder. The outer interleaver interleaves at least selected data 
bits across the selected number of the frames of the data bits. An inner 
encoder is coupled to be provided with the frames of data bits once 
interleaved by the outer interleaver. The inner encoder encodes at least 
selected data bits of each frame of the selected number of the frames of 
the data bits. An inner interleaver is coupled to be provided with the 
frames of data bits once encoded by the inner encoder. The inner 
interleaver interleaves at least selected data bits across the selected 
number of the frames of the data bits. 
A more complete appreciation of the present invention and the scope thereof 
can be obtained from the accompanying drawings which are briefly 
summarized below, the following detailed description of the 
presently-preferred embodiments of the invention, and the appended claims.

DETAILED DESCRIPTION OF THE PRESENT INVENTION 
Referring first to FIG. 1, a portion of a cellular communication system, 
shown generally at 10, illustrates a network infrastructure portion 12 and 
a single mobile terminal 14. The infrastructure portion 12 and the mobile 
terminal 14 are interconnected by way of a communication channel 16 which 
forms a link therebetween. The channel 16 may, e.g., be susceptible to 
multi-path fading. 
It should be noted at the outset that, while the various embodiments of the 
present invention shall be described with respect to a cellular 
communication system, the present invention can similarly be embodied in 
other types of wireless communication systems, such as, e.g., an RLL 
(Radio in the Local Loop) communication system or a satellite 
communication system. The present invention can be embodied in other full 
duplex communication systems, as well as half-duplex, and simplex 
communication systems. 
During operation of the cellular communication system 10, communication 
signals are transmitted between the infrastructure portion 12 and the 
mobile terminal 14. An embodiment of the present invention is operable to 
improve the radio link performance of the system. Data bits, formatted 
into frames, which are to be communicated between the portion 12 and the 
mobile terminal 14 are interleaved and encoded. Once interleaved and 
encoded, the bits are modulated upon a carrier wave. Interleaving and 
encoding facilitates their re-creation at a receiving station subsequent 
to transmission upon a communication channel which exhibits interference, 
such as that caused by multi-path fading. 
An information signal, here shown functionally to be generated by an 
information source 22, is provided by way of line 24 to a source encoder 
and formatter 26. The source encoder 26, in one embodiment, digitizes the 
information signal applied thereto and formats digitized data bits into 
frames. A source-encoded signal generated by the encoder 26 is applied, by 
way of line 28, to an outer channel encoder 32. Line 33 extending to the 
outer channel encoder 32 is further illustrated in the figure. Data bits 
formed of internal-control, signaling bits are also selectively provided 
to the encoder 32 on the line 33. 
In one embodiment, as shall be described below, the outer channel encoder 
32 forms a block encoder for block encoding the data bits of the signal 
applied thereto according to a selected block encoding technique. Through 
such block encoding, the redundancy of the data bits of the signal applied 
thereto is increased. While the exemplary embodiment illustrates the 
encoder 32 to be formed of a block encoder, in other embodiments, the 
encoder encodes the bits of the signal applied thereto in other manners. 
The outer channel encoder 32 is coupled, by way of line 34, to an outer 
interleaver 36. The outer interleaver 36 is operable to interleave groups 
of bits across successive ones of the frames into which the data bits are 
formatted by the source encoder and formatter 26. The outer encoder 32 and 
the outer interleaver 36 provide a first stage of encoding and 
interleaving of the data bits of the signal generated by the information 
source 22. 
The outer interleaver 36 is coupled by way of line 38 to an inner encoder 
42. The inner encoder 42, in one embodiment, forms a convolutional encoder 
for convolutionally encoding the signal applied thereto. The inner encoder 
is here further operable to encode the data bits of each frame applied to 
the encoder. While the exemplary embodiment illustrates the encoder 42 to 
be formed of a convolutional encoder, in other embodiments, the encoder 
encodes the bits of the signal applied thereto in other manners. 
The inner encoder is coupled by way of line 44 to an inner interleaver 46. 
The inner interleaver is operable to interleave data bits across 
successive ones of the frames of data bits applied thereto. The inner 
encoder 42 and the inner interleaver 46 together form a second stage of 
encoding and interleaving of the information signal. 
The encoders 32 and 42 and interleavers 36 and 46 together form the 
apparatus 50 of an embodiment of the present invention for forming a 
multi-stage interleaved and encoded communication signal. In one 
embodiment, the apparatus 50 is formed at a radio base station of a 
cellular communication system. 
The inner interleaver 46 is coupled by way of line 51 to a modulator 52. 
The modulator 52 is operable to modulate the signal applied thereto 
according to a modulation technique, such as, e.g., a GMSK (Gaussian 
Minimum Shift Keying) modulation or a QPSK (Quadrature Phase Shift Keying) 
modulation technique. Typically, for CDMA-based systems, spreading of the 
coded and interleaved bits by a code (spreading) sequence is performed 
prior to modulation. Correspondingly, subsequent to demodulation, a 
despreading is performed. In conventional manner, the modulator is 
operable to modulate the signal applied thereto upon a carrier wave, 
thereby to form a communication signal of characteristics to permit its 
transmission upon the communication channel 16. As illustrated in the 
figure, the communication channel 16 includes a plurality of paths 54 upon 
which the communication signal is transmitted to the mobile terminal 14. 
Because the communication channel 16 includes multiple numbers of paths, 
the communication signal is susceptible to fading during its transmission 
thereon. 
The mobile terminal 14 includes demodulator circuitry 56 for demodulating 
the communication signal received at the mobile terminal 14. The 
demodulator 56 is operable in a manner generally reverse to that of the 
modulator 52. The demodulator 56 generates a digitized signal on line 58 
which is applied to an inner deinterleaver 62. 
The inner deinterleaver 62 is operable in a manner generally reverse to 
that of the inner interleaver 46 to deinterleave bits of the signal 
applied thereto. 
The inner deinterleaver 62 is coupled by way of line 64 to an inner decoder 
66. The inner decoder is operable in a manner generally reverse to that of 
the inner encoder 42 to convolutionally decode the signal applied thereto. 
The inner deinterleaver 62 and the inner decoder 66 perform a first stage 
of deinterleaving and decoding of the signal received by the mobile 
terminal 14, once demodulated by the demodulator 56. 
The inner decoder 66 is coupled by way of lines 68 to an outer 
deinterleaver 72. The outer deinterleaver 72 is operable in a manner 
generally reverse to that of the outer interleaver 36. The outer 
deinterleaver deinterleaves groups of bits of the signal applied thereto. 
The outer deinterleaver 72 is coupled by way of lines 74 to an outer 
channel decoder 76. The outer channel decoder is operable in a manner 
generally reverse to that of the outer channel encoder 32. The outer 
channel encoder is operable to block decode groups of bits of the signal 
applied thereto. 
The inner and outer deinterleavers 62 and 72 and inner and outer decoders 
66 and 76 together form the apparatus 80 of an embodiment of the present 
invention for deinterleaving and decoding a multi-stage interleaved and 
encoded signal. 
The outer channel decoder 76 is coupled by way of line 81 to a source 
decoder 82. The source decoder is operable in a manner generally reverse 
to that of the source encoder 26 and generates a source-decoded signal on 
line 84 which is applied to an information sink 86. 
Full duplex communication is permitted between the network infrastructure 
portion 12 and the mobile terminal 14. The network infrastructure portion 
12 includes receiver circuitry, here represented by block 88, which is 
generally functional in a manner analogous to the elements forming the 
receiver circuitry of the mobile terminal 14. And, analogously, the mobile 
terminal 14 includes transmitter circuitry, represented by the block 92, 
which is operable in manners similar to the elements of the transmitter 
circuitry shown to form a portion of the network infrastructure portion 
12. 
The multi-stage encoding and interleaving of the information signal 
generated by the information source 22 increases the possibility that the 
informational content of the information signal can be recreated even if 
the communication channel 16 upon which the modulated communication 
transmitted by the portion 12 exhibits significant levels of multi-path 
fading. 
Appropriate coding and interleaving operations performed upon the data bits 
of the information signal generated by the information source 22 provide 
bit error rate performance good enough to permit the transmission of data. 
Data transmission requiring such a high radio link performance might be 
required in mobile radio environments to transmit, for instance, wireless 
multimedia, required to perform worldwide web browsing and also video 
transmissions. 
As mentioned previously, encoding and interleaving operations introduce 
transmission delay. Such transmission delay results from the need both to 
encode and interleave the data bits as well as to decode and deinterleave 
the data bits. Additionally, to perform such operations across more than 
one frame typically requires that such successive frames be buffered for 
purposes of performing the interleaving, as well as deinterleaving, 
operations. When the outer interleaving and inner interleaving operation 
functions are performed separately, buffering of sequences of frames of 
the information signal is typically required before the performance of 
such operations. Analogously, when the inner and outer deinterleaving 
operations are performed as separate functions, separate buffering is 
required prior to the performance of such deinterleaving operations. 
However, by performing outer and inner interleaving across the same number 
of frames permits a reduction in the transmission delay as only a single 
buffering stage is required to perform the interleaving operations and a 
single buffering stage is required to perform the deinterleaving 
operations. That is to say, a reduction in the transmission delay is 
permitted if an N number of frames across which outer interleaving is 
performed corresponds in number with a K number of frames across which 
inner interleaving is performed, i.e., N=K. 
In an embodiment of the present invention, the encoders 32 and 42 and the 
interleavers 36 and 46 are positioned together at a single logical device, 
and the outer and inner interleavers 36 and 46 are operable to perform 
separate interleaving functions over the same group of frames. A 
co-working functionality between such operations is provided. Because the 
outer and inner interleaver are operable over the same number of frames, 
only a single buffering stage is required to buffer the frames over which 
the interleaving is to be performed. 
Similarly, only a single buffering stage is required at the mobile terminal 
to perform both inner and outer deinterleaving operations. Thereby, the 
transmission delay accompanied with a second buffering stage is obviated. 
The interleaving span of the inner interleaver can be made as long as the 
span of the outer interleaver, all without affecting the total delay 
significantly. By making the size of the inner interleaver as large as 
possible for a given total delay, the performance of the transmission 
scheme is optimized. 
FIGS. 2A-D illustrate the various transmission delays caused by operation 
of selected elements forming a portion of the communication system 10 
shown in FIG. 1. Review of such figures illustrates the variance in 
transmission delay resulting from selection of the links of the frames 
upon which interleaving and encoding, and corresponding deinterleaving and 
decoding, operations are performed and the functional locations at which 
such operations are performed. 
First, FIG. 2A illustrates the transmission delay introduced between the 
inner encoder and interleaver 42-56 and inner deinterleaver and decoder 
62-66. The total transmission delay T.sub.D1 is as follows. 
EQU T.sub.D1 =T.sub.F +T.sub.Piei +T.sub.Pidd 
wherein: 
T.sub.Piei : processing delay of the inner encoder and interleaver 
T.sub.F : frame delay 
T.sub.Pidd : processing delay of the inner decoder and deinterleaver. 
FIG. 2B illustrates an additional portion of the communication 10 shown in 
FIG. 1. Here, again, the elements 42-46 and 62-66 are again illustrated. 
In FIG. 2B, the outer encoder and interleaver 36-50 and outer 
deinterleaver and decoder 72-76 are further illustrated. The transmission 
delay T.sub.D2, when K=1 can be represented as: 
EQU T.sub.D2 =2NT.sub.F +T.sub.F +T.sub.Piei +T.sub.Pidd +T.sub.Poei +T.sub.Pod 
d 
wherein: 
T.sub.Poei : processing delay of the outer encoder and interleaver 
T.sub.Podd : processing delay of the outer decoder and deinterleaver 
and wherein the remaining terms are as defined previously. 
FIG. 2C illustrates the same structure as that illustrated in FIG. 2B. 
Here, however, the transmission delay T.sub.D3 is shown when K=N. The 
transmission delay T.sub.D3 is as follows: 
EQU T.sub.D3 =2NT.sub.F +(2N-1) T.sub.F +NT.sub.Piei +NT.sub.Pidd +T.sub.Poei 
+T.sub.Podd 
wherein the elements are as defined previously. 
FIG. 2D illustrates again the structure shown previously in FIGS. 2B and 
2C. Here, however, the functionality of such elements are performed at 
single logical devices at the transmit and receive sides of the 
communication system. The transmission delay, T.sub.D4 is as follows: 
EQU T.sub.D4 =2NT.sub.F +NT.sub.Piei +NT.sub.Pidd +T.sub.Poei +T.sub.Podd 
wherein the terms as defined previously. 
Comparison of the various transmission delays illustrates that the 
transmission delay associated with the structures shown in FIG. 2D is 
roughly the same as that shown in 2B whereas, in contrast, the structures 
shown in FIG. 2C has about twice the amount of delay as that of FIG. 2D. 
FIG. 3 illustrates the apparatus 50 in greater detail. Again, the apparatus 
is shown to include an outer channel encoder 32 coupled to receive a 
source-encoded signal generated on line 28. The apparatus is here shown to 
include a buffer 102 for buffering N frames of data. Once buffered, groups 
of data bits of the frame buffered by the buffer 102 are encoded by the 
outer encoder 32 and interleaved by the interleaver 36 across frames of 
the data. Thereafter, and as described previously, the data bits are 
encoded by the inner encoder 42 and interleaved by the inner interleaver 
46. The apparatus 50 is further shown to include a control device 104, 
coupled to the encoders 32 and 42, the interleavers 36 and 46, and the 
buffer 102 by way of control lines 106. The control device 104 is 
operable, inter alia, to select and otherwise control the coding rates of 
the encoders, to select and control the manners by which the interleavers 
are operable, such as, e.g., the interleaving depth and width, and to 
select and control the number of N frames buffered by the buffer 102. The 
control device provides, e.g., the ability to recreate later, 
service-specified tailored encoding and interleaving schemes. The control 
device 104 thereby forms a code rate selector and frame number selector 
and is able also to control the width and depth of both the outer and 
inner interleaving as well as the group size of the groups that the outer 
interleaver interleaves. 
FIG. 4 illustrates in greater detail the apparatus 80, shown previously in 
FIG. 1. Here, a buffer 108 is positioned between the line 58 and the inner 
deinterleaver 62. The buffer 108 buffers N frames of the demodulated 
signal formed by the demodulator 56 (shown in FIG. 1). Data bits of the 
frames of data bits buffered by the buffer 108 are deinterleaved by the 
inner deinterleaver 62 and decoded by the decoder 66. In one embodiment, 
the N-frame buffering can be performed in the inner deinterleaver and a 
separate device 108 is not necessary. Then, as described previously, 
groups of data bits of the frames of data bits are deinterleaved by the 
outer deinterleaver 72, and block decoding of groups of the data bits of 
the frames of data bits is effectuated by the outer decoder 76. The 
apparatus 80 is further shown to include a control device 114, coupled to 
the decoders 66 and 76, the deinterleavers 62 and 72, and the buffer 108 
by way of the control lines 116. The control device 114 is operable, inter 
alia, to select and control the decoding rates of the decoders, to select 
and control the manners by which the deinterleavers are operable, and to 
select the number of N frames buffered by the buffer 108. 
Because the same number of frames of data bits are interleaved by the outer 
and inner interleavers 36 and 46 and deinterleaved by the deinterleavers 
62 and 72, the frames are required to be buffered only once during 
generation of the communication signal and only once during recovery of 
the informational content once received at the apparatus 80. 
FIG. 5 illustrates operation of an exemplary block coder, also shown at 32, 
of which the outer channel encoder 32 might be formed. Examples of block 
codes are Reed-Solomon codes and BCH (Bose, Chadhuri, Hocquenhem) codes. 
As illustrated in the figure, a message block of data bits are applied, 
here by way of line 128 to the block encoder 32. The block encoder 32 
generates a code block 133 on line 134, here illustrated to be formed of 
both the message block 130 and check bits 135. The check bits 135 are 
dependent upon values of the data bits of the message block 130. While not 
separately shown, the decoder 76 can be analogously formed to be operable 
in a manner generally reverse to that shown in FIG. 5. 
FIG. 6 illustrates an exemplary convolutional encoder, also shown at 42, of 
which the inner encoder 42 may be comprised. Input line 138 is coupled to 
the encoder 42 to provide message blocks 139 of data bits to the encoder. 
In a convolutional encoder, code symbols generated by the encoder are of 
values dependent not only upon the digits in a current message block 
shifted into the encoder but also upon values of message blocks previously 
applied to the encoder. 
In the exemplary illustration of FIG. 6, each bit of the message blocks 139 
applied to the encoder 42 is coded into two bits which form a coded 
information stream 143 generated on line 144. While not separately shown, 
the decoder 66 can be analogously formed to be operable in a manner 
generally reverse to that shown in FIG. 6. 
FIG. 7 illustrates operation of an exemplary block interleaver to 
interleave data bits of frames of data together. In the example shown, a 
data bit stream 150 is split into rows of data bit streams and arranged in 
a matrix-like manner in stage 152. The data bit stream is here of a length 
of at least N frames of signal bits. 
The data stream 150 is thus read-in-row-wise. The interleaved data bit 
stream 154 is then generated by column-wise reading out from stage 152, 
the data bits, as shown in FIG. 7. 
The number of rows in the stage 152, define the interleaving depth and the 
number of columns define the interleaving width of the interleaver. In 
this example the interleaving width is 12 and the interleaving depth is 
four. By interleaving the data bits in such manner, a fading dip exhibited 
upon a communication channel upon which the interleaved signal is 
transmitted does not result in the loss of an entire frame of the input 
data bits; rather, individual bits of several of the frames are lost. 
Recovery of the informational content of a frame is more likely if only 
small portions of the informational content of a frame are lost. Although 
FIG. 7 illustrates an operation of a block interleaving, other types of 
interleaving, such as for example convolutional interleaving, could also 
be considered, along with the control possibilities that such an 
interleaving offers. 
While not separately shown, interleaving of groups of data bits, such as 
groups of eight data bits, can similarly be interleaved amongst successive 
frames of data bits. Deinterleaver operations, such as those performed by 
the deinterleavers 62 and 72 are generally reverse to the interleaver 
operation illustrated in the figure. 
FIG. 8 illustrates a method, shown generally at 170, of an embodiment of 
the present invention. The method is operable to encode and interleave a 
communication signal to be transmitted by a communication station upon a 
communication channel. The communication signal is formed of successive 
frames of data bits. 
First, as indicated by the block 172, at least selected data bits are 
encoded across a selected number of the successive frames of the data bits 
of the communication signal. 
Then, and as indicated by the block 174, at least selected data bits are 
interleaved across the selected number of the successive frames of the 
data bits of the communication signal. 
Then, and as indicated by the block 176, at least selected data bits of 
each frame of the selected number of the successive frames of the data 
bits are encoded. 
And, as indicated by the block 178, at least selected data bits are 
interleaved across the selected number of the successive frames of the 
data bits. 
By encoding and interleaving the communication signal in such a manner, the 
possibility that the informational content of the communication signal can 
be recovered even if transmitted upon a communication channel which 
exhibits significant levels of fading is more likely to be possible. 
A method of an embodiment of the present invention is analogously operable 
to decode and deinterleave a multi-stage, encoded and interleaved signal. 
The steps of such a method are generally the reverse of those method steps 
illustrated in FIG. 8. 
The need to ensure that the informational content of a communication signal 
transmitted upon a communication channel can be recovered with little or 
no error is particularly important when the informational content 
comprises data to be transmitted to a receiving station. 
Operation of an embodiment of the present invention in a wireless 
communication system permits improved radio link performance without an 
undue increase in the transmission delay otherwise required to provide 
multi-stage encoding and interleaving. As the multi-stage encoding and 
interleaving can be performed at a single logical device, the entire 
interleaving and encoding operations may be performed at a radio base 
station which forms a downlink signal to be transmitted to a mobile 
terminal. Analogous circuitry formed at a mobile terminal permits recovery 
of the informational content of the downlink signal transmitted thereto. 
And, circuitry of the mobile terminal also permits the generation of 
multi-stage encoded and interleaved signals for transmission to a base 
station. 
The previous descriptions are of preferred examples for implementing the 
invention, and the scope of the invention should not necessarily be 
limited by this description. The scope of the present invention is defined 
by the following claims.