Transmission of a plurality of channels for CDMA telecommunications system

BACKGROUND OF THE INVENTION

I. Field of the Invention

0001The present invention relates to wireless telecommunications. More particularly, the present invention relates to a novel and improved method for implementing a high-transmission-rate over-the-air interface.

II. Description of the Related Art

0002The IS-95 standard from the Telecommunications Industry Association (TIA), and its derivatives such as IS-93A and ANSI J-STD-008 (referred to herein collectively as IS-95), define an over-the-air interface suitable for implementing a bandwidth-efficient digital cellular telephone system. To this end, IS-95 provides a method for establishing multiple radio frequency (RF) traffic channels, each having a data transmission rate of up to 14.4 kilobits per second. The traffic channels can be used for conducting voice telephony or for conducting digital data communications including small file transfer, electronic mail, and facsimile.

0003While 14.4 kilobits per second is adequate for these types of lower data rate applications, the increasing popularity of more data intensive applications such as worldwide web and video conferencing has created a demand for much higher transmission rates. To satisfy this new demand, the present invention is directed towards providing an over-the-air interface capable of higher transmission rates.

0004<figref idref="f0001"><b>FIG. 1</b></figref> illustrates a highly simplified digital cellular telephone system configured in a manner consistent with the use of IS-95. During operation, telephone calls and other communications are conducted by exchanging data between subscriber units <b>10</b> and base stations <b>12</b> using RF signals. The communications are further conducted from base stations <b>12</b> through base station controllers (BSC) <b>14</b> and mobile switching center (MSC) <b>16</b> to either public switch telephone network (PSTN) <b>18,</b> or to another subscriber unit 10. BSC's <b>14</b> and MSC <b>16</b> typically provide mobility control, call processing, and call routing functionality.

0005In an IS-95 compliant system, the RF signals exchanged between subscriber units <b>10</b> and base stations <b>12</b> are processed in accordance with code division multiple access (CDMA) signal processing techniques. The use of CDMA signal processing techniques allows adjacent base stations <b>12</b> to use the same RF bandwidth which, when combined with the use of transmit power control, makes IS-95 more bandwidth efficient than other cellular telephone systems.

0006CDMA processing is considered a "spread spectrum" technology because the CDMA signal is spread over a wider amount of RF bandwidth than is generally used for non-spread spectrum systems. The spreading bandwidth for an IS-95 system is 1.2288 MHz. A CDMA-based digital wireless telecommunications system configured substantially in accordance with the use of IS-95 is described in <patcit id="pcit0001" dnum="US5103459A"><text>US Patent 5,103,459</text></patcit> entitled "SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM," assigned to the assignee of the present invention.

0007It is anticipated that the demand for higher transmission rates will be greater for the forward link than for the reverse link because a typical user is expected to receive more data than he or she generates. The forward link signal is the RF signal transmitted from a base station <b>12</b> to one or more subscriber units <b>10.</b> The reverse link signal is the RF signal transmitted from subscriber unit <b>10</b> to a base station <b>12.</b>

0008<figref idref="f0002"><b>FIG. 2</b></figref> illustrates the signal processing associated with an IS-95 forward link traffic channel, which is a portion of the IS-95 forward link signal. The forward link traffic channel is used for the transmission of user data from a base station <b>12</b> to a particular subscriber unit <b>10.</b> During normal operation, the base station <b>12</b> generates multiple forward link traffic channels, each of which is used for communication with a particular subscriber unit <b>10.</b> Additionally, the base station <b>12</b> generates various control channels including a pilot channel, a sync channel, and a paging channel. The forward link signal is the sum of the traffic channels and control channels.

0009As shown in <figref idref="f0002"><b>FIG. 2</b></figref><b>,</b> user data is input at node <b>30</b> and processed in 20 millisecond (ms) blocks called frames. The amount of data in each frame may be one of four values with each lower value being approximately half of the next higher value. Also, two possible sets of frame sizes can be utilized, which are referred to as rate set one and rate set two.

0010For rate set two the amount of data contained in the largest, or "full-rate," frame corresponds to a transmission rate of 13.35 kilobits per second. For rate set one the amount of data contained in the full rate frame corresponds to a transmission rate of 8.6 kilobits per second. The smaller sized frames are referred to as half-rate, quarter-rate, and eighth-rate frames. The various frame rates are used to adjust for the changes in voice activity experienced during a normal conversation.

0011CRC generator <b>36</b> adds CRC data with the amount of CRC data generated dependent on the frame size and rate set. Tail byte generator <b>40</b> adds eight tail bits of known logic state to each frame to assist during the decoding process. For full-rate frames, the number of tail bits and CRC bits brings the transmission rate up to 9.6 and 14.4 kilobits per second for rate set one and rate set two.

0012The data from tail byte generator <b>40</b> is convolutionally encoded by encoder <b>42</b> to generate code symbols <b>44.</b> Rate 1/2, constraint length (K) 9, encoding is performed.

0013Puncture <b>48</b> removes 2 of every 6 code symbols for rate set two frames, which effectively reduces the encoding performed to rate 2/3. Thus, at the output of puncture <b>48</b> code symbols are generated at 19.2 kilosymbols per second (ksps) for both rate set one and rate set two full-rate frames.

0014Block interleaver <b>50</b> performs block interleaving on each frame, and the interleaved code symbols are modulated with a Walsh channel code from Walsh code generator <b>54</b> generating sixty-four Walsh symbols for each code symbol. A particular Walsh channel code W_i is selected from a set of sixty-four Walsh channel codes and typically used for the duration of an interface between a particular subscriber unit <b>10</b> and a base station <b>12.</b>

0015The Walsh symbols are then duplicated, and one copy is modulated with an in-phase PN spreading code (PN_I) from spreading code generator <b>52,</b> and the other copy is modulated with a quadrature-phase PN spreading code (PN_Q) from spreading code generator 53. The in-phase data is then low-pass filtered by LPF <b>58</b> and modulated with an in-phase sinusoidal carrier signal. Similarly, the quadrature-phase data is low-pass filtered by LPF <b>60</b> and modulated with a quadrature-phase sinusoidal carrier. The two modulated carrier signals are then summed to form signal s(t) and transmitted as the forward link signal.

SUMMARY OF THE INVENTION

0016The present invention is a novel and improved method for implementing a high-transmission-rate over-the-air interface. A transmit system provides an in-phase channel set and a quadrature-phase channel set. The in-phase channel set is used to provide a complete set of orthogonal medium rate control and traffic channels. The quadrature-phase channel set is used to provide a high-rate supplemental channel and an extended set of medium rate channels that are orthogonal to each other and the original medium rate channels. The high-rate supplemental channel is generated over a set of medium rate channels using a short channel code. The medium rate channel are generated using a set of long channel codes.

BRIEF DESCRIPTION OF THE DRAWINGS

0017The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001"><b>FIG.1</b></figref> is a block diagram of a cellular telephone system;</li><li><figref idref="f0002"><b>FIG. 2</b></figref> is a block diagram of the forward link signal processing associated with the IS-95 standard;</li><li><figref idref="f0003"><b>FIG. 3</b></figref> is a block diagram of a transmit system configured in accordance with one embodiment of the invention;</li><li><figref idref="f0004 f0005 f0006"><b>FIG. 4</b></figref> is a list of the set of 64-symbol Walsh codes and associated indexes used in a preferred embodiment of the invention.</li><li><figref idref="f0007"><b>FIG. 5</b></figref> is a block diagram of the channel coding performed in accordance with one embodiment of the invention;</li><li><figref idref="f0008"><b>FIG. 6</b></figref> is a block diagram of a receive system configured in accordance with one embodiment of the invention; and</li><li><figref idref="f0007"><b>FIG. 7</b></figref> is a block diagram of a decoding system configured in accordance with one embodiment of the invention.</li></ul>

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

0018<figref idref="f0003"><b>FIG. 3</b></figref> is a block diagram of a transmit system configured in a manner consistent with use of the invention. Typically, the transmit system will be used to generated the forward link signal in a cellular telephone system and therefore would be incorporated into a base station <b>12.</b> In the exemplary configuration shown, the transmit system generates a forward link signal that includes a complete set of IS-95, or medium rate, channels as well as a high-speed supplemental channel. Additionally, in the embodiment described, an extended set of IS-95 channels is provided. Alternative embodiments of the invention could provide more than one high-speed supplemental channel, or not provide the use of an additional set of IS-95 channels, or both. Also, while providing IS-95 channels is preferred, other embodiments of the invention may incorporate other channel types and processing protocols.

0019In the exemplary embodiment provided, the transmit system provides an in-phase channel set <b>90</b> and a quadrature-phase channel set <b>92.</b> The in-phase channel set <b>90</b> is used to provide the complete set of orthogonal IS-95 control and traffic channels. Orthogonal channel to not interfere with one another when transmitted via the same path. The quadrature-phase channel set <b>92</b> is used to provide a high-rate supplemental channel and an extended set of IS-95 channels that are orthogonal to each other and the original IS-95 channels. In the preferred embodiment of the invention, all the signals and data shown in <figref idref="f0003"><b>FIG. 3</b></figref> are formed by positive and negative integer values represented by binary digital data or voltages, which correspond to a logic low and a logic high, respectively.

0020For the in-phase channel set <b>90,</b> IS-95 control channel system <b>100</b> performs various functions associated with one of the standard IS-95 control channels including encoding and interleaving, the processing of which is described in IS-95 incorporated herein by reference. In this case, since the Walsh₁ channel code is used, the processing will be in accordance with the use of a paging channel. The resulting code symbols from IS-95 control channel system <b>100</b> are modulated with a Walsh code from Walsh₁ generator <b>102</b> by multiplier <b>104.</b> The Walsh generators <b>102</b> are used to generate the orthogonal in-phase channels.

0021Walsh generator <b>102</b> repeatedly generates a Walsh code of index 1 (Walsh₁) from a set of Walsh codes of indexes 0 to 63 (Walsh_0-63). <figref idref="f0004 f0005 f0006"><b>FIG. 4</b></figref> is a list of the set of 64-symbol Walsh codes and associated indexes used in a preferred embodiment of the invention. A Walsh chip corresponds to a Walsh symbol and a Walsh chip value of 0 corresponds to a positive (+) integer while a Walsh chip value of 1 corresponds to a negative (-) integer. Under IS-95 Walsh₁ code corresponds to the paging channel. The Walsh symbols generated by modulation with the Walsh₁ code are gain adjusted by channel gain <b>108</b>(2).

0022The pilot channel is generated by gain adjusting a positive 1 value using channel gain <b>108</b>(1). No encoding is performed for the pilot channel in accordance with IS-95, as the Walsh₀ code used for the pilot channel is all plus 1 values, and therefore equivalent to no modulation at all.

0023Additional control channels are generated in similar fashion using additional IS-95 control channel systems, additional Walsh generators, and additional channel gains (all not shown). Such control channels include a synchronization channel, which is modulated with the Walsh₃₂ code. The processing associated with each type of IS-95 control channel is described in IS-95.

0024The processing associated with one of the IS-95 traffic channels in the in-phase channel set is illustrated with IS-95 traffic channel system 110, which performs various functions associated with an IS-95 traffic channel including convolutional encoding and interleaving as described above to generate a sequence of symbols at 19.2 kilosymbols per second. The code symbols from IS-95 traffic channel system <b>110</b> are modulated with the 64-symbol Walsh₆₃ code from Walsh₆₃ generator <b>112</b> by multiplier <b>114</b> to generate a sequence of symbols at 1.2288 Megasymbols per second. The Walsh symbols from multiplier <b>114</b> are gain adjusted by gain adjust 108(64).

0025The outputs of all gain adjusts including gain adjusts <b>108</b>(1) <b>-</b> (64) are summed by summer <b>120</b> generating in-phase data D_I. Each gain adjust 108 increases or decreases the gain of the particular channel with which it is associated. The gain adjust can be performed in response to a variety of factors including power control commands from the subscriber unit 10 processing the associated channel, or to differences in the type of data being transmitted over the channel. By keeping the transmit power of each channel at the minimum necessary for proper communication, interference is reduced and the total transmit capacity increased. In one embodiment of the invention, gain adjusts <b>108</b> are configured by a control system (not shown) which could take the form of a microprocessor.

0026Within quadrature-phase channel set <b>92,</b> an extended set of 64 - 2^N IS-95 traffic channels are provided using IS-95 channel systems <b>124.</b> N is a integer value based on the number of Walsh channels allocated for the supplemental channel and is described in greater detail below. Each code symbols from the IS-95 channel systems <b>124</b>(2) - (64 - 2^N) is modulated with a Walsh code from Walsh generators <b>126</b> by multipliers <b>128,</b> except for IS-95 traffic channel system <b>124(1),</b> which is placed on Walsh₀ channel, and therefore does not require modulation.

0027To provide the high-rate supplemental channel, supplemental channel system <b>132</b> generates code symbols at a rate R_S, which is 2^N times that of a full-rate IS-95 traffic channel. Each code symbol is modulated with a supplemental Walsh code (Walsh_S) from supplemental Walsh code generator <b>134</b> using multiplier 140. The output of multiplier <b>140</b> is gain adjusted by gain adjust <b>130.</b> The outputs of the set of gain adjusts <b>130</b> are summed by summer <b>150</b> yielding quadrature-phase data D_Q. It should be understood that the extended set of IS-95 traffic channel could be completely or partially replaced with one or more additional supplemental channels.

0028The processing performed by supplemental channel system <b>132</b> is described in greater detail below. The Walsh_s code generated by supplemental Walsh code generator <b>134</b> depends the number of Walsh codes allocated for the high-rate supplemental channel in quadrature-phase channel set 92. In the preferred embodiment of the invention, the number of Walsh channels allocated for the high-rate supplemental channel can be any value 2^N where N = {2, 3, 4, 5, 6}. The Walsh_s codes are 64/2^N symbols long, rather than the 64 symbols used with the IS-95 Walsh codes. In order for the high-rate supplemental channel to be orthogonal to the other quadrature-phase channels with 64-symbol Walsh codes, 2^N of the possible 64 quadrature-phase channels with 64-symbol Walsh codes cannot be used for the other quadrature-phase channels. Table I provides a list of the possible Walsh_s codes for each value of N and the corresponding sets of allocated 64-symbol Walsh codes. <tables id="tabl0001" num="0001"><table frame="all"><title><b>Table I.</b></title><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="10mm" /><colspec colnum="2" colname="col2" colwidth="49mm" /><colspec colnum="3" colname="col3" colwidth="56mm" /><thead><row><entry align="center" valign="top"><b>N</b></entry><entry align="center" valign="top"><b>Walsh_i</b></entry><entry align="center" valign="top"><b>Allocated 64-Symbol Walsh Codes</b></entry></row></thead><tbody><row rowsep="0"><entry morerows="15" rowsep="1" align="center"><b>2</b></entry><entry align="center"><b>+,+,+,+,+,+,+,+,+,+,+,+,+,+,+,+</b></entry><entry align="center"><b>0, 16, 32, 48</b></entry></row><row rowsep="0"><entry align="center"><b>+,-,+,-,+,-,+,-,+,-,+,-,+,-,+,-</b></entry><entry align="center"><b>1, 17, 33, 49</b></entry></row><row rowsep="0"><entry align="center"><b>+,+,-,-,+,+,-,-,+,+,-,-,+,+,-,-</b></entry><entry align="center"><b>2, 18, 34, 50</b></entry></row><row rowsep="0"><entry align="center"><b>+,-,-,+,+,-,-,+,+,-,-,+,+,-,-,+</b></entry><entry align="center"><b>3, 19, 35, 51</b></entry></row><row rowsep="0"><entry align="center"><b>+,+,+,+,-,-,-,-,+,+,+,+,-,-,-,-</b></entry><entry align="center"><b>4, 20, 36, 52</b></entry></row><row rowsep="0"><entry align="center"><b>+,-,+,-,-,+,-,+,+,-,+,-,-,+,-,+</b></entry><entry align="center"><b>5, 21, 37, 53</b></entry></row><row rowsep="0"><entry align="center"><b>+,+,-,-,-,-,+,+,+,+,-,-,-,-,+,+</b></entry><entry align="center"><b>6, 22, 38, 54</b></entry></row><row rowsep="0"><entry align="center"><b>+,-,-,+,-,+,+,-,+,-,-,+,-,+,+,-</b></entry><entry align="center"><b>7, 23, 39, 55</b></entry></row><row rowsep="0"><entry align="center"><b>+,+,+,+,+,+,+,+,-,-,-,-,-,-,-,-</b></entry><entry align="center"><b>8, 24, 40, 56</b></entry></row><row rowsep="0"><entry align="center"><b>+,-,+,-,+,-,+,-,-,+,-,+,-,+,-,+</b></entry><entry align="center"><b>9,25,41,57</b></entry></row><row rowsep="0"><entry align="center"><b>+,+,-,-,+,+,-,-,-,-,+,+,-,-,+,+</b></entry><entry align="center"><b>10,26,42,58</b></entry></row><row rowsep="0"><entry align="center"><b>+,-,-,+,+,-,-,+,-,+,+,-,-,+,+,-</b></entry><entry align="center"><b>11, 27, 43, 59</b></entry></row><row rowsep="0"><entry align="center"><b>+,+,+,+,-,-,-,-,-,-,-,-,+,+,+,+</b></entry><entry align="center"><b>12,28,44,60</b></entry></row><row rowsep="0"><entry align="center"><b>+,-,+,-,-,+,-,+,-,+,-,+,+,-,+,-</b></entry><entry align="center"><b>13, 29, 45, 61</b></entry></row><row rowsep="0"><entry align="center"><b>+,+,-,-,-,-,+,+,-,-,+,+,+,+,-,-</b></entry><entry align="center"><b>14,30,46,62</b></entry></row><row><entry align="center"><b>+,-,-,+,-,+,+,-,-,+,+,-,+,-,-,+</b></entry><entry align="center"><b>15, 31, 47, 63</b></entry></row><row rowsep="0"><entry morerows="7" rowsep="1" align="center"><b>3</b></entry><entry align="center"><b>+,+,+,+,+,+,+,+</b></entry><entry align="center"><b>0, 8, 16, 24, 32, 40, 48, 56</b></entry></row><row rowsep="0"><entry align="center"><b>+,-,+,-,+,-,+,-</b></entry><entry align="center"><b>1, 9,17, 25, 33, 41, 49, 57</b></entry></row><row rowsep="0"><entry align="center"><b>+,+,-,-,+,+,-,-</b></entry><entry align="center"><b>2, 10, 18, 26, 34, 42, 50, 58</b></entry></row><row rowsep="0"><entry align="center"><b>+,-,-,+,+,-,-,+</b></entry><entry align="center"><b>3, 11, 19, 27, 35, 43, 51, 59</b></entry></row><row rowsep="0"><entry align="center"><b>+,+,+,+,-,-,-,-</b></entry><entry align="center"><b>4, 12, 20, 28, 36, 44, 52, 60</b></entry></row><row rowsep="0"><entry align="center"><b>+,-,+,-,-,+,-,+</b></entry><entry align="center"><b>5, 13, 21, 29, 37, 45, 53, 61</b></entry></row><row rowsep="0"><entry align="center"><b>+,+,-,-,-,-,+,+</b></entry><entry align="center"><b>6, 14, 22, 30, 38, 46, 54, 62</b></entry></row><row><entry align="center"><b>+,-,-,+,-,+,+,-</b></entry><entry align="center"><b>7, 15, 23, 31, 39, 47, 55, 63</b></entry></row><row rowsep="0"><entry morerows="3" rowsep="1" align="center"><b>4</b></entry><entry align="center"><b>+,+,+,+</b></entry><entry align="center"><b>0, 4, 8,...,60</b></entry></row><row rowsep="0"><entry align="center"><b>+,-,+,-</b></entry><entry align="center"><b>1, 5, 9, ...,61</b></entry></row><row rowsep="0"><entry align="center"><b>+,+,-,-</b></entry><entry align="center"><b>2, 6, 10, ...,62</b></entry></row><row><entry align="center"><b>+,-,-,+</b></entry><entry align="center"><b>3, 7, 11, ...,63</b></entry></row><row rowsep="0"><entry morerows="1" rowsep="1" align="center"><b>5</b></entry><entry align="center"><b>+,+</b></entry><entry align="center"><b>0, 2, 4,...,62</b></entry></row><row><entry align="center"><b>+,-</b></entry><entry align="center"><b>1, 3, 5, ...,63</b></entry></row><row><entry align="center"><b>6</b></entry><entry align="center"><b>+</b></entry><entry align="center"><b>0,1,2,...,63</b></entry></row></tbody></tgroup></table></tables>

0029The + and - indicate a positive or negative integer value, where the preferred integer is 1. As is apparent, the number of Walsh symbols in each Walsh_s code varies as N varies, and in all instances is less than the number of symbols in the IS-95 Walsh channel codes. Thus, the supplemental channel is formed using a short Walsh channel code and the IS-95 channels are formed using longer Walsh channel codes. Regardless of the length of the Walsh_s code, in the described embodiment of the invention the symbols are applied at a rate of 1.2288 Megachips per second (Mcps). Thus, shorter length Walsh_s codes are repeated more often.

0030Data channels D_I and D_Q are complex multiplied, as the first real and imaginary terms respectively, with spreading codes PN_I and PN_Q, as the second real and imaginary terms respectively, yielding in-phase (or real) term X_I and quadrature-phase (or imaginary) term X_Q. Spreading codes PN_I and PN_Q are generated by spreading code generators 152 and 154. Spreading codes PN_I and PN_Q are applied at 1.2288 Mcps. Equation (1) illustrates the complex multiplication performed. <maths id="math0001" num="(1)"><math display="block"><mfenced><msub><mi mathvariant="normal">X</mi><mi mathvariant="normal">I</mi></msub><mo mathvariant="normal">+</mo><msub><mi>jX</mi><mi mathvariant="normal">Q</mi></msub></mfenced><mo mathvariant="normal">=</mo><mfenced><msub><mi mathvariant="normal">D</mi><mi mathvariant="normal">I</mi></msub><mo mathvariant="normal">+</mo><msub><mi>jD</mi><mi mathvariant="normal">Q</mi></msub></mfenced><mo>⁢</mo><mfenced><msub><mi>PN</mi><mi mathvariant="normal">I</mi></msub><mo mathvariant="normal">+</mo><msub><mi>jPN</mi><mi mathvariant="normal">Q</mi></msub></mfenced></math><img file="EP1802004B1_D0001.tif" /></maths>

0031In-phase term X_I is then low-pass filtered to a 1.2288 MHz bandwidth (not shown) and upconverted by multiplication with in-phase carrier COS(ω_ct). Similarly, quadrature-phase term X_Q is low-pass filtered to a 1.2288 MHz bandwidth (not shown) and upconverted by multiplication with quadrature-phase carrier SIN(ω_ct). The upconverted X_I and X_Q terms are summed yielding forward link signal s(t).

0032The complex multiplication allows quadrature-phase channel set <b>92</b> to remain orthogonal to the in-phase channel set <b>90</b> and therefore to be provided without adding additional interference to the other channels transmitted over the same path with perfect receiver phase recovery. Thus, a complete set of sixty-four Walsh_i channels is added in an orthogonal manner to the original IS-95 channel set, and this channel set can be used for the supplemental channel. Additionally, by implementing the supplemental channel in the orthogonal quadrature-phase channel set <b>92,</b> a subscriber unit <b>10</b> configured to process the normal IS-95 forward link signal will still be able to processes the IS-95 channels within in-phase channel set 90 thus providing the high-transmission-rate channel while maintaining backwards compatibility with previously existing systems.

0033While the embodiment of the invention shown in <figref idref="f0003"><b>FIG. 3</b></figref> uses a single set of in-phase and quadrature-phase carriers to generate the in-phase and quadrature-phase channel set, separate sets of sinusoids could be used to independently generate the in-phase and quadrature-phase channel sets, with the second set of carriers offset from the first set by 90°. For example, the D_Q data could be applied to the second set of carrier sinusoids where the D_Q in-phase (PNI) spread data is applied to COS(ω_ct-90°) and the D_Q quadrature-phase (PNQ) spread data is applied to SIN(ω_ct-90°). The resulting signals are then summed to produce the quadrature-phase channel set 92, which in turn are summed with the in-phase channel set 90.

0034The use of the Walsh_s channels as set forth in Table I. also allows simplified implementation of the supplemental channel within quadrature-phase channel set <b>92</b>. In particular, the use of the Walsh_s codes listed in Table I allows the supplemental channel to use whole subsets of 64 symbol Walsh_i codes without the need to generate each and everyone of those Walsh codes.

0035For example, when N = 5 the Walsh_s codes specified by Table I allocate a set of 32 64-symbol Walsh_i codes for the supplemental channel. That is, all the even-indexed 64-symbol Walsh codes or all of the odd-indexed 64-symbol Walsh codes are allocated for the supplemental channel. This leaves the odd-indexed or even-index channels, respectively, for implementing the extended IS-95 traffic channel set. In <figref idref="f0003"><b>FIG. 3</b></figref>, the supplemental channel uses the odd 64-symbol Walsh code channels when Walsh_s = {+,-} and the even channels are available for the extended IS-95 traffic channel set.

0036In another example, when N = 4, the associated Walsh_s codes allocate a set of sixteen 64-symbol Walsh_i codes. This leaves a set of forty-eight remaining Walsh_i codes for implementing the extended IS-95 traffic channels or for implementing additional supplemental channels. In general, the use of the Walsh_s code that corresponds to a particular value N allocates 2^N 64-symbol Walsh_i codes for the supplemental channel using only a single, and shorter, Walsh_s code.

0037The allocation of whole subsets of Walsh_i codes using a single Walsh_s code is facilitated by even distribution the 64-symbol Walsh_i codes within the subset. For example, when N = 5 the Walsh_i codes are separated by 2, and when N = 4 the Walsh_i codes are separated by 4. Only by providing a complete set of quadrature-phase channels 92 for implementing the supplemental channel can the allocation of large set of evenly spaced Walsh_i channels be performed, and therefore implemented using a single Walsh_s code.

0038Also, allocating a subset of 64-symbol Walsh_i codes using a single shorter Walsh_s code reduces the complexity associated with providing a high-rate supplemental channel. For example, performing actual modulation using the set of 64-symbol Walsh_i codes, and summing of the resulting modulated data would require a substantial increase in signal processing resources when compared with the use of the single Walsh_s generator used in the implementation of the invention described herein.

0039Sets of evenly spaces Walsh_i channels could not be allocated as easily if the supplemental channel were placed in the in-phase channel set <b>90</b> of the previously existing IS-95 forward link, or in the in-phase and quadrature-phase channels with QPSK modulation. This is because certain sixty-four symbol Walsh_i channels are already allocated for control functions such as the paging, pilot, and sync channels on the in-phase channel. Thus, using a new quadrature-phase Walsh code space allows for simplified implementation of the supplemental channel.

0040Also, the use of the a single Walsh_s code improves the performance of the high-rate supplemental channel because the variance in the amplitude of the supplemental channel is minimized. In the embodiment described herein, the amplitude is simply based on the positive or negative integer associated with the Walsh_s code. This is in contrast to performing the modulation with a set of 2^N 64-symbol Walsh_i codes, which would result in the set of amplitudes 0, +2, -2, +4, -4,...,2^N, and -2^N.

0041Among other improvements, reducing the variance in the amplitude reduces the peak-to-average power ratio, which increases the range at which the forward link signal can be received for a given maximum transmit power of the base station <b>12,</b> or other forward link transmit system.

0042<figref idref="f0007"><b>FIG. 5</b></figref> is a block diagram of the supplemental channel system <b>132</b> of <figref idref="f0001"><b>FIG. 1</b></figref> when configured in accordance with one embodiment of the invention. User data is received by CRC checksum generator <b>200</b> which adds checksum information to the data received. In the preferred embodiment of the invention, the data is processed in 20 ms frames as is performed for IS-95, and 16 bits of checksum data is added. Tail bits <b>202</b> adds eight tail bits to each frame. The output of tail bits <b>202</b> is received at a data rate D by convolutional encoder <b>204</b> which performs convolutional encoding at rate R_c on each frame. R_c differs for different embodiments of the invention as described in greater detail below.

0043Block interleaver <b>206</b> interleaves the code symbols from convolutional encoder <b>204</b> and repeater <b>208</b> repeats the code symbol sequence from interleaver <b>206</b> by a repeat amount M. The repeat amount M varies in different embodiments of the invention, and will typically depend on the coding rate R_c and the supplemental channel rate R_S (see <figref idref="f0003"><b>FIG. 3</b></figref>). The repeat amount is discussed further below. Mapper <b>210</b> receives the code symbols from repeater <b>208</b> and converts the logic zeros and logic ones into positive and negative integer values which are output at the supplemental channel rate R_s.

0044Table II provides a list of data input rates D, encoding rates R_c, repeat amounts M, and supplemental channel rates R_s that can be used in different embodiments of the invention. In some embodiments multiple rates are used. <tables id="tabl0002" num="0002"><table frame="all"><title><b>Table II.</b></title><tgroup cols="8"><colspec colnum="1" colname="col1" colwidth="25mm" /><colspec colnum="2" colname="col2" colwidth="10mm" /><colspec colnum="3" colname="col3" colwidth="21mm" /><colspec colnum="4" colname="col4" colwidth="25mm" /><colspec colnum="5" colname="col5" colwidth="20mm" /><colspec colnum="6" colname="col6" colwidth="22mm" /><colspec colnum="7" colname="col7" colwidth="25mm" /><colspec colnum="8" colname="col8" colwidth="23mm" /><thead><row><entry align="center" valign="top">Convolutional Encoder Input Rate (D) kbps</entry><entry align="center" valign="top">(N)</entry><entry align="center" valign="top">Walsh Channels for Supp. Channel (2^N)</entry><entry align="center" valign="top">Convolutional Code Rate (R_c)</entry><entry align="center" valign="top">Repetition Amount (M)</entry><entry align="center" valign="top">Walsh Symbols/ Code Symbols (W/S)</entry><entry align="center" valign="top">Convolutional Encoder Input Bits</entry><entry align="center" valign="top">Number of Channel Bits per Frame</entry></row></thead><tbody><row rowsep="0"><entry align="center">38.4</entry><entry align="center">2</entry><entry align="center">4</entry><entry align="center">_1/2</entry><entry align="center">1</entry><entry align="center">16/1</entry><entry align="center">768</entry><entry align="center">1,536</entry></row><row rowsep="0"><entry align="center">38.4</entry><entry align="center">3</entry><entry align="center">8</entry><entry align="center">_1/4</entry><entry align="center">1</entry><entry align="center">8/1</entry><entry align="center">768</entry><entry align="center">3,072</entry></row><row rowsep="0"><entry align="center">38.4</entry><entry align="center">4</entry><entry align="center">16</entry><entry align="center">_1 /4</entry><entry align="center">2</entry><entry align="center">4/1</entry><entry align="center">768</entry><entry align="center">6,144</entry></row><row rowsep="0"><entry align="center">38.4</entry><entry align="center">5</entry><entry align="center">32</entry><entry align="center">_1/4</entry><entry align="center">4</entry><entry align="center">2/1</entry><entry align="center">768</entry><entry align="center">12,288</entry></row><row><entry align="center">38.4</entry><entry align="center">6</entry><entry align="center">64</entry><entry align="center">_1/4</entry><entry align="center">8</entry><entry align="center">1/1</entry><entry align="center">768</entry><entry align="center">24,576</entry></row><row rowsep="0"><entry align="center">76.8</entry><entry align="center">3</entry><entry align="center">8</entry><entry align="center">_1/2</entry><entry align="center">1</entry><entry align="center">8/1</entry><entry align="center">1,536</entry><entry align="center">3,072</entry></row><row rowsep="0"><entry align="center">76.8</entry><entry align="center">4</entry><entry align="center">16</entry><entry align="center">_1/4</entry><entry align="center">1</entry><entry align="center">4/1</entry><entry align="center">1,536</entry><entry align="center">6,144</entry></row><row rowsep="0"><entry align="center">76.8</entry><entry align="center">5</entry><entry align="center">32</entry><entry align="center">_1/4</entry><entry align="center">2</entry><entry align="center">2/1</entry><entry align="center">1,536</entry><entry align="center">12,288</entry></row><row><entry align="center">76.8</entry><entry align="center">6</entry><entry align="center">64</entry><entry align="center">_1/4</entry><entry align="center">4</entry><entry align="center">1/1</entry><entry align="center">1,536</entry><entry align="center">24,576</entry></row><row rowsep="0"><entry align="center">153.6</entry><entry align="center">4</entry><entry align="center">16</entry><entry align="center">_1/2</entry><entry align="center">1</entry><entry align="center">4/1</entry><entry align="center">3,072</entry><entry align="center">6,144</entry></row><row rowsep="0"><entry align="center">153.6</entry><entry align="center">5</entry><entry align="center">32</entry><entry align="center">1/4</entry><entry align="center">1</entry><entry align="center">2/1</entry><entry align="center">3,072</entry><entry align="center">12,288</entry></row><row><entry align="center">153.6</entry><entry align="center">6</entry><entry align="center">64</entry><entry align="center">_1/4</entry><entry align="center">2</entry><entry align="center">1/1</entry><entry align="center">3,072</entry><entry align="center">24,576</entry></row></tbody></tgroup></table></tables>

0045Three encoder input rates D for the supplemental channel are shown: 38.4, 76.8, and 153.6 kilobits per second. For each of these encoder input rates D, a set of encoder rates R_c, N values, and repeat amounts M are provided which achieve the desired encoder input rate D. Additionally, the ratio of Walsh_s symbols to code symbols is provided, which corresponds to the length of the Walsh_s code. Also, the number of encoder input bits per 20 frame is provided, as is the number of code symbols transmitted per 20 ms frame. The actual data transmission rate will be equal to the encoder input rate D, less the overhead necessary for the CRC bits and tail bits and any other control information provided. The use of Reed-Soloman encoding in addition to, or instead of, CRC checksum encoding is also contemplated.

0046In general, it is desirable to use the largest value of N possible for the supplemental channel in order to spread the supplemental channel over the greatest number of Walsh_i channels. Spreading the supplemental channel out over a larger set of Walsh_i channels minimizes the effect of inter-channel interference between the two corresponding Walsh_i channels on the in-phase channel set <b>90</b> and the quadrature-phase channel set <b>92</b>. This inter-channel interference is created by imperfect phase alignment experienced during receive processing. By spreading out the supplemental channel over a larger set of Walsh; channels, the amount of inter-channel interference experience for any particular Walsh_i channel in the in-phase channel set 90 is minimized, because the portion of the supplemental channel in that Walsh_i channel is small. Also, spreading the supplemental channel over a larger set of Walsh_i channels with a larger total channel symbol rate allows for a higher symbol diversity, which improves performance in fading channel conditions.

0047When the number of Walsh channels needed for the desired encoder input rate D using rate 1/2 encoding is less than the number of available Walsh channels by at least a factor of two, performance is improved by spreading the signal over more Walsh channels. The higher channel symbol rate for the larger number of Walsh channels is obtained by using a rate 1/4, rather than a rate 1/2, code, or by sequence repetition, or both. The rate 1/4 code provides additional coding gain over that of a rate 1/2 code in benign and fading channel conditions and the sequence repetition provides improved performance in fading channel conditions due to the increased diversity.

0048In a preferred embodiment of the invention, a supplemental channel having an encoder input rate of 76.8 kilobits per second is provided using N = 5, an encoder rate R_c of 1/4, and a repetition amount of M = 2. Such an implementation provides data transfer rates on the order of an ISDN channel including sufficient bandwidth for signaling. Also, using N = 5 maintains 32 additional Walsh_i channels for providing extended IS-95 channels.

0049The actual sustainable transmission rate of the supplemental channel will vary depending on a variety of environmental conditions including the amount of multipath experienced by the forward link transmission. The supplemental transmission rate depends of the amount of multipath because forward link signals that arrive via different paths are no longer orthogonal and therefore interfere with one another. This interference increases with increased transmission rates because of the additional transmit power necessary. Thus, the more multipath interference experienced, the less the sustainable transmission rate of the supplemental channel. Therefore, a lower transmission rate for the supplemental channel is preferred for high multipath environments.

0050In one embodiment of the invention, a control system that measures the various environmental factors and which selects the optimal supplemental channel processing characteristics is contemplated. Also, the use of signal cancellation is contemplated for removing noise due to multipath transmissions. A method and apparatus for performing such noise cancellation is described in copending <patcit id="pcit0002" dnum="US518217A" dnum-type="L"><text>US patent application serial no. 08/518,217</text></patcit> entitled "METHOD AND SYSTEM FOR PROCESSING A PLURALITY OF MULTIPLE ACCESS TRANSMISSIONS" assigned to the assignee of the present invention and incorporated herein by reference.

0051<figref idref="f0008"><b>FIG. 6</b></figref> is a block diagram of a receive processing system for processing the high-rate supplemental channel in accordance with one embodiment of the invention. Typically, the receive processing system will be implemented in a subscriber unit <b>10</b> of a cellular telephone system.

0052During operation, RF signals received by antenna system <b>300</b> are downconverted with in-phase carrier <b>302</b> and quadrature-phase carrier <b>304</b> generating digitized in-phase receive samples R_I and quadrature-phase receive samples R_Q. These receive samples are provided to the finger processor module shown and to other finger processors (not shown) in accordance with the use of a rake receiver. Each finger processor processes one instance of the supplemental forward link signal received, with each instance generated by multipath phenomena.

0053The in-phase and quadrature-phase receive samples R_I and R_Q are multiplied with the complex conjugate of the PN spreading codes generated by in-phase spreading code generator <b>306</b> and quadrature-phase spreading code generator <b>308</b> yielding receive terms Y_I and Y_Q. The receive terms Y_I and Y_Q are modulated with the Walsh_s code generated by Walsh generator <b>310,</b> and the resulting modulated data is summed over the number of Walsh symbols in the Walsh_s code by summers <b>312.</b> Additionally, the receive terms Y_I and Y_Q are summed and filtered (averaged) by pilot filters <b>316.</b>

0054The outputs of summers <b>312</b> are then multiplied with the complex conjugate of the filter pilot data, and the resulting quadrature-phase term is used at the supplemental channel soft-decision data <b>320.</b> Supplemental soft-decision data <b>320</b> can then be combined with soft-decision data from other finger processors (not shown) and the combined soft-decision data decoded.

0055<figref idref="f0007"><b>FIG. 7</b></figref> is a block diagram of decoder system used to decode the supplemental soft-decision data <b>320</b> in accordance with one embodiment of the invention. The soft-decision data is received by accumulator <b>400</b> which accumulates samples of the soft-decision data by the repeat amount M. The accumulated data is then deinterleaved by block deinterleaver <b>402</b> and decoded by trellis decoder <b>404.</b> Various types of decoders are well known including Viterbi decoders.

0056The user data in the hard-decision data from trellis decoder <b>404</b> is then checked with the CRC checksum data by CRC check system <b>406,</b> and the resulting user data is output along with check results indicating whether the user data was consistent with the check sum data. The receive processing system or user can then determine whether to use the user data based on the CRC checksum results.

0057Thus, a high data rate transmission system particularly suited for use in conjunction with the IS-95 forward link has been described. The invention can be incorporated into both terrestrial as well as satellite based wireless communication systems, as well as wire based communication systems over which sinusoidal signals are transmitted such as coaxial cable systems. Also, while the invention is described in the context of a 1.2288 MHz bandwidth signal, the use of other bandwidths is consistent with the operation of the invention including 2.5 MHz and 5.0 MHz systems.

0058Similarly, while the invention is described using transmission rates on the order of 10 kbps and 70 kbps, the use of other channel rates may be employed. In a preferred embodiment of the invention, the various systems described herein are implemented using semiconductor integrated circuits coupled via conduct, inductive, and capacitive connections, the use of which is well known in the art.