Round trip delay adjustment in multipoint-to-point communication using orthogonal frequency division multiplexing Number:7,426,177 from the United States Patent and Trademark Office (PTO) owispatent Systems and methods for bidirectional communication are provided. In one embodiment, a method for aligning communications from a plurality of remote units in a multipoint-to-point orthogonal frequency division multiplexed (OFDM) communications comprises sending a first signal from a host unit to a first remote unit; receiving a second signal transmitted from the first remote unit in response to the first signal; generating at least one timing adjustment signal based at least in part on a round trip delay between the sending of the first signal and the receiving of the second signal; transmitting the timing adjustment signal to the first remote unit; wherein the timing adjustment signal instructs the first remote unit to delay OFDM transmission of data to improve alignment of multiframes at the host unit when communications are received at the host unit from the plurality of remote units.<H communication, multiplexing, Round, trip, dela, 7426177.html, Patent, pto, 7426177

Title: Round trip delay adjustment in multipoint-to-point communication using orthogonal frequency division multiplexing

Abstract: Systems and methods for bidirectional communication are provided. In one embodiment, a method for aligning communications from a plurality of remote units in a multipoint-to-point orthogonal frequency division multiplexed (OFDM) communications comprises sending a first signal from a host unit to a first remote unit; receiving a second signal transmitted from the first remote unit in response to the first signal; generating at least one timing adjustment signal based at least in part on a round trip delay between the sending of the first signal and the receiving of the second signal; transmitting the timing adjustment signal to the first remote unit; wherein the timing adjustment signal instructs the first remote unit to delay OFDM transmission of data to improve alignment of multiframes at the host unit when communications are received at the host unit from the plurality of remote units.

Patent Number: 7,426,177 Issued on 09/16/2008 to Geile, et al.

Inventors: Geile; Michael J. (Loveland, OH), Brede; Jeffrey (Eden Prairie, MN)
Assignee: ADC Telecommunications Inc. (Eden Prairie, MN)

Appl. No.: 11/687,383

Filed: March 16, 2007

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
11420851	May., 2006
09903273	Jun., 2006	7069577
09397443	Aug., 2001	6279158
08673002	Dec., 2001	6334219
08650408	May., 1996
08457295	Jun., 1995
08457317	Jun., 1995
08384659	Feb., 1995

Current U.S. Class: 370/206 ; 370/203; 370/204; 370/207; 370/208; 370/312; 370/328; 370/338; 370/346; 370/347; 375/130; 375/133; 375/141; 375/147

Current International Class: H04J 11/00 (20060101)

References Cited [Referenced By]

U.S. Patent Documents


3780230	December 1973	Bowen et al.
4101738	July 1978	Bellanger et al.
4472802	September 1984	Pin et al.
4494228	January 1985	Gutleber
4495619	January 1985	Acampora
4503533	March 1985	Tobagi et al.
4516170	May 1985	Skerlos
4519074	May 1985	Basile
4528656	July 1985	Morais
4646296	February 1987	Bartholet et al.
4710918	December 1987	Miyao
4731816	March 1988	Hughes-Hartogs
4774707	September 1988	Raychaudhuri
4783779	November 1988	Takahata et al.
4799252	January 1989	Eizenhoffer et al.
4807259	February 1989	Yamanaka et al.
4821120	April 1989	Tomlinson
4847880	July 1989	Kamerman et al.
4853686	August 1989	Kueng et al.
4912721	March 1990	Pidgeon, Jr. et al.
4977612	December 1990	Wilson
4985902	January 1991	Gurcan
5005169	April 1991	Bronder et al.
5025485	June 1991	Csongor et al.
5038342	August 1991	Crisler et al.
5063574	November 1991	Moose
5073899	December 1991	Collier et al.
5088111	February 1992	McNamara et al.
5103459	April 1992	Gilhousen et al.
5128625	July 1992	Yatsuzuka et al.
5128967	July 1992	Durkin et al.
5166924	November 1992	Moose
5173899	December 1992	Ballance
5175867	December 1992	Wejke et al.
5181106	January 1993	Sutherland
5197061	March 1993	Halbert-Lassalle et al.
5204874	April 1993	Falconer et al.
5206886	April 1993	Bingham
5228062	July 1993	Bingham
5235615	August 1993	Omura
5240851	August 1993	Paridans et al.
5255290	October 1993	Anvari
5276703	January 1994	Budin et al.
5276706	January 1994	Budin et al.
5282222	January 1994	Fattouche et al.
5285474	February 1994	Chow et al.
5291289	March 1994	Hulyalkar et al.
5297186	March 1994	Dong
5321542	June 1994	Freitas et al.
5327455	July 1994	De Gaudenzi et al.
5327575	July 1994	Menich et al.
5343209	August 1994	Sennott et al.
5345439	September 1994	Marston
5345440	September 1994	Gledhill et al.
5349580	September 1994	Hester et al.
5357502	October 1994	Castelain et al.
5371548	December 1994	Williams
5371780	December 1994	Amitay
5375140	December 1994	Bustamante et al.
5390216	February 1995	Bilitza et al.
5400322	March 1995	Hunt et al.
5406551	April 1995	Saito et al.
5420851	May 1995	Seshadri et al.
5423067	June 1995	Manabe
5425027	June 1995	Baran
5425050	June 1995	Schreiber et al.
5444697	August 1995	Leung et al.
5446727	August 1995	Bruckert et al.
5469468	November 1995	Schilling
5471464	November 1995	Ikeda
5483529	January 1996	Baggen et al.
5483550	January 1996	Hulbert
5488412	January 1996	Majeti et al.
5499236	March 1996	Giallorenzi et al.
5499241	March 1996	Thompson et al.
5504773	April 1996	Padovani et al.
5504775	April 1996	Chouly et al.
5519706	May 1996	Bantz et al.
5519731	May 1996	Cioffi
5521943	May 1996	Dambacher
5528621	June 1996	Heiman et al.
5533008	July 1996	Grube et al.
5534913	July 1996	Majeti et al.
5537414	July 1996	Takiyasu et al.
5548582	August 1996	Brajal et al.
5550812	August 1996	Philips
5559833	September 1996	Hayet
5581555	December 1996	Dubberly et al.
5588022	December 1996	Dapper et al.
5590403	December 1996	Cameron et al.
5594726	January 1997	Thompson et al.
5600672	February 1997	Oshima et al.
5600754	February 1997	Gardner et al.
5602836	February 1997	Papadopoulos et al.
5603081	February 1997	Raith et al.
5606576	February 1997	Dapper et al.
5608764	March 1997	Sugita et al.
5613193	March 1997	Ishikawa et al.
5619504	April 1997	Van Grinsven et al.
5621753	April 1997	Weber
5625651	April 1997	Cioffi
5627863	May 1997	Aslanis et al.
5644573	July 1997	Bingham et al.
5650997	July 1997	Yang et al.
5652772	July 1997	Isaksson et al.
5673292	September 1997	Carlin
5680388	October 1997	Kahre
5694389	December 1997	Seki et al.
5699365	December 1997	Klayman et al.
5703873	December 1997	Ojanpera et al.
5726973	March 1998	Isaksson
5732068	March 1998	Takahashi et al.
5748677	May 1998	Kumar
5764706	June 1998	Carlin et al.
5768309	June 1998	Olafsson
5784363	July 1998	Engstrom et al.
5793759	August 1998	Rakib et al.
5793772	August 1998	Burke et al.
5802044	September 1998	Baum et al.
5802241	September 1998	Oshima
5815488	September 1998	Williams et al.
5815794	September 1998	Williams
5838799	November 1998	Cioffi et al.
5859876	January 1999	Dapper et al.
5867764	February 1999	Williams
5898732	April 1999	Dapper et al.
5903546	May 1999	Ikeda et al.
5943361	August 1999	Gilhousen et al.
RE36430	December 1999	Halbert-Lassalle et al.
6018528	January 2000	Gitlin et al.
6157669	December 2000	Kotzin
6219840	April 2001	Corrigan et al.
6275990	August 2001	Dapper et al.
6279158	August 2001	Geile et al.
6330241	December 2001	Fort
6366585	April 2002	Dapper et al.
6415133	July 2002	Brede et al.
6430417	August 2002	Raith et al.
6467092	October 2002	Geile et al.
6487258	November 2002	Jedwab et al.
6496982	December 2002	Johansson et al.
6594322	July 2003	Dapper et al.
7068678	June 2006	Cioffi et al.
7069577	June 2006	Geile et al.
7071994	July 2006	Harris et al.
7280564	October 2007	Geile et al.
2001/0050926	December 2001	Kumar
2004/0012387	January 2004	Shattil
2007/0192815	August 2007	Geile et al.

Foreign Patent Documents


0725509	Aug., 1996	EP
9203384	Oct., 1993	SE
9203384-4	Oct., 1993	SE
9216063	Sep., 1992	WO
9411961	May., 1994	WO

Other References

Engstrom et al., "A System for Test of Multiaccess Methods Based on OFDM", "Conference Proceedings, 1994 IEEE 44th Vehicular Technology Conference", Jun. 8-10, 1994, pp. 1843-1845, vol. 3, Publisher: IEEE, Published in: Stockholm, Sweden. cited by other .
Sari et al., "An analysis of Orthogonal Frequency-Division Multiple Access", "Global Telecommunications Conference", 1997, pp. 1635-1639, vol. 3, Publisher: IEEE. cited by other .
Wei et al., "Synchronization Requirements for Multi-User OFDM On Satellite Mobile and Two-Path Rayleigh Fading Channels","IEEE Transactions on Communications", Feb. - Apr., 1995, pp. 887-895, vol. 83, No. 2-4, IEEE, Published in New York, NY. cited by other .
Cimini, Leonard J. "Analysis and Simulation of a Digital Mobile Channel Using Orthogonal Frequency Division Multiplexing". IEEE. Transactions on Communications, Jul. 1985, pp. 665-675, vol. 33, No. 7. Publisher: IEEE. Published in: New York City. cited by other.

Primary Examiner: Jain; Raj K.
Attorney, Agent or Firm: Fogg & Powers LLC

Parent Case Text

CROSS REFERENCE TO RELATED CASES

This application is a continuation of application Ser. No. 11/420,851 filed on May 30, 2006, entitled "DYNAMIC BANDWIDTH ALLOCATION" (currently pending), which is a divisional of application Ser. No. 09/903,273 filed Jul. 11, 2001, entitled "DYNAMIC BANDWIDTH ALLOCATION" (now U.S. Pat. No. 7,069,577), which is a continuation of application Ser. No. 09/397,443, filed Sep. 15, 1999, entitled "DYNAMIC BANDWIDTH ALLOCATION" (now U.S. Pat. No. 6,279,158), which is a divisional of U.S. application Ser. No. 08/673,002 filed Jun. 28, 1996 (now U.S. Pat. No. 6,334,219) which is a continuation-in-part of U.S. application Ser. No. 08/650,408 filed May 20, 1996 (abandoned), Ser. No. 08/457,295 filed Jun. 1, 1995 (abandoned), Ser. No. 08/457,317 filed Jun. 1, 1995 (abandoned), and Ser. No. 08/384,659 filed Feb. 6, 1995 (abandoned) whose applications are incorporated herein by reference.

This application is related to U.S. application Ser. No. 08/311,964 filed Sep. 26, 1994 (abandoned), Ser. No. 08/455,340 filed May 31, 1995 (abandoned), Ser. No. 08/455,059 filed May 31, 1995 (abandoned), Ser. No. 08/457,294 filed Jun. 1, 1995 (abandoned), Ser. No. 08/457,110 filed Jun. 1, 1995 (abandoned), Ser. No. 08/456,871 filed Jun. 1, 1995 (abandoned), Ser. No. 08/457,022 filed Jun. 1, 1995 (abandoned), and Ser. No. 08/457,037 filed Jun. 1, 1995 (abandoned), whose applications are incorporated herein by reference.

Claims

What is claimed is:

1. A multipoint-to-point, orthogonal frequency division multiplexed (OFDM) communication system comprising: a plurality of remote units; a host unit that includes a demodulator; wherein each of the remote units transmits an upstream OFDM signal using a multiple access scheme to the host unit demodulator using at least one of a plurality of orthogonal tones within an OFDM waveform, wherein upstream OFDM signals from at least two of the plurality of remote units combine to a unified OFDM waveform at the host unit; wherein the host unit receives the upstream OFDM signals from a plurality of the remote units, the tones of the upstream signals being substantially orthogonal when received at the host unit; wherein portions of upstream OFDM signals from at least two of the remote units arrive at the host unit at the same time; wherein the host unit demodulator demodulates said portions; wherein the host unit detects a round trip delay between the host unit and each remote unit; and wherein the host unit transmits at least one timing adjustment signal to at least one of the remote units based at least in part on at least one of the detected round trip delays to assist in aligning the upstream signals received by the host unit; wherein the host unit detects a round trip delay between the host unit and each remote unit at least one of iteratively, repeatedly, and periodically to assist in maintaining alignment of signals at the host unit within the OFDM communication system.

2. The OFDM communication system of claim 1 wherein the system is used in a hybrid fiber coax network.

3. The OFDM communication system of claim 1 wherein the system is used in a wireless network.

4. The OFDM communication system of claim 1 wherein the host unit compares the round trip delay of a first remote unit to a reference value before transmitting the timing adjustment signal.

5. The OFDM communication system of claim 1 wherein the at least one timing adjustment signal instructs the at least one remote unit to delay transmission of its upstream signal to assist in aligning its upstream signal at the host unit with upstream signals from other remote units.

6. The OFDM communication system of claim 1 wherein the at least one remote unit makes a timing adjustment based at least in part on the timing adjustment signal from the host unit, and wherein the timing adjustment assists in achieving multiframe alignment at the host unit with upstream signals from other remote units in the OFDM communication system.

7. A system comprising: a host unit; a plurality of remote units using a multiple access scheme to communicate at the same time with the host unit using orthogonal frequency division multiplexing (OFDM), wherein upstream OFDM signals from at least two of the plurality of remote units combine to a unified OFDM waveform at the host unit; wherein each of the at least two of the plurality of remote units transmits the upstream OFDM signals on at least one distinct tone of a plurality of orthogonal tones within the unified OFDM waveform; wherein portions of the upstream OFDM signals from the at least two of the plurality of remote units arrive at the host unit at the same time; wherein the host unit determines a round trip delay between the host unit and at least one remote unit; and wherein the host unit uses the round trip delay to send a timing instruction to at least one of the remote units to improve alignment of multiframes received at the host unit from the plurality of remote units; wherein the host unit determines a round trip delay between the host unit and the at least one remote unit at least one of iteratively, repeatedly, and periodically to assist in maintaining alignment of multiframes received at the host unit from the plurality of remote units.

8. The system of claim 7 further comprising a distribution network wherein the host unit communicates with the plurality of remote units using the distribution network, wherein the distribution network comprises at least one of a hybrid fiber coax network and a wireless system.

9. The system of claim 7 wherein the host unit determines the round trip delay by timing the interval between transmission of a first signal from the host unit to the remote unit and receipt of a response signal at the host unit from the remote unit.

10. The system of claim 7 wherein the host unit uses the round trip delay to send a timing instruction to at least one of the remote units so that multiframes received at the host unit from the plurality of remote units are aligned.

11. A method for aligning communications from a plurality of remote units in a multipoint-to-point orthogonal frequency division multiplexed (OFDM) communications system, the method comprising: receiving a first signal from a host unit at a first remote unit; sending a second signal from the first remote unit based on the first signal; wherein a time in which the second signal is sent is based on the first signal; receiving at least one timing adjustment signal at the first remote unit from the host unit, the timing adjustment signal based on the second signal; wherein the timing adjustment signal instructs the first remote unit to delay OFDM transmission of data based on a time of arrival of the second signal at the host unit to improve alignment of multiframes at the host unit when communications are received at the host unit from the plurality of remote units; and wherein the first remote unit is configured to share between a plurality of remote units an Orthogonal Frequency Division Multiplexing (OFDM) waveform for communicating with the host unit; wherein an upstream OFDM signal from the first remote unit is configured to combine with an upstream OFDM signal from at least one other remote unit to a unified OFDM waveform at the host unit; wherein the first remote unit receives a timing adjustment signal at least one of iteratively, repeatedly, and periodically to assist in maintaining alignment of multiframes at the host unit when communications are received at the host unit from the plurality of remote units.

12. The method of claim 11 wherein each of the first signal, the second signal, and the timing adjustment signal are transmitted over a distribution network that comprises at least one of a hybrid fiber coax network and a wireless system.

13. The method of claim 11 wherein the at least one timing adjustment signal comprises a path delay adjustment value that brings a round trip path delay for the first remote unit closer to that of other remote units in the system.

Description

BACKGROUND

Information services found in households and businesses today include television (or video) services and telephone services. Another information service involves digital data transfer which is most frequently accomplished using a modem connected to a telephone service. All further references to telephony herein shall include both telephone services and digital data transfer service.

Characteristics of telephony and video signals are different and therefore telephony and video networks are designed differently as well. For example, telephony information occupies a relatively narrow band when compared to the bandwidth for video signals. In addition, telephony signals are low frequency whereas NTSC standard video signals are transmitted at carrier frequencies greater than 50 MHz. Accordingly, telephone transmission networks are relatively narrow band systems which operate at audio frequencies and which typically serve the customer by twisted wire drops from a curb-side junction box. On the other hand, cable television services are broad band and incorporate various frequency carrier mixing methods to achieve signals compatible with conventional very high frequency television receivers. Cable television systems or video services are typically provided by cable television companies through a shielded cable service connection to each individual home or business.

One attempt to combine telephony and video services into a single network is described in U.S. Pat. No. 4,977,593 to Balance entitled "Optical Communications Network." Balance describes a passive optical communications network with an optical source located in a central station. The optical source transmits time division multiplexed optical signals along an optical fiber and which signals are later split by a series of splitters between several individual fibers servicing outstations. The network allows for digital speech data to be transmitted from the outstations to the central station via the same optical path. In addition, Balance indicates that additional wavelengths could be utilized to add services, such as cable television, via digital multiplex to the network.

A 1988 NCTA technical paper, entitled "Fiber Backbone: A Proposal For an Evolutionary Cable TV network Architecture," by James A. Chiddix and David M. Pangrac, describes a hybrid optical fiber/coaxial cable television (CATV) system architecture. The architecture builds upon existing coaxial CATV networks. The architecture includes the use of a direct optical fiber path from a head end to a number of feed points in an already existing CATV distribution system.

U.S. Pat. No. 5,153,763 to Pidgeon, entitled "CATV Distribution Networks Using Light Wave Transmission Lines," describes a CATV network for distribution of broad band, multichannel CATV signals from a head end to a plurality of subscribers. Electrical to optical transmitters at the head end and optical to electrical receivers at a fiber node launch and receive optical signals corresponding to broad band CATV electrical signals. Distribution from the fiber node is obtained by transmitting electrical signals along coaxial cable transmission lines. The system reduces distortion of the transmitted broad band CATV signals by block conversion of all or part of the broad band of CATV signals to a frequency range which is less than an octave. Related U.S. Pat. No. 5,262,883 to Pidgeon, entitled "CATV Distribution Networks Using Light Wave Transmission Lines," further describes the distortion reducing system.

Although the above-mentioned networks describe various concepts for transmitting broad band video signals over various architectures, which may include hybrid optical fiber/coax architectures, none of these references describe a cost effective, flexible, communications system for telephony communications. Several problems are inherent in such a communication system.

One such problem is the need to optimize the bandwidth used for transporting data so that the bandwidth used does not exceed the allotted bandwidth. Bandwidth requirements are particularly critical in multi-point to point communication where multiple transmitters at remote units must be accommodated such that allotted bandwidth is not exceeded.

A second problem involves power consumption of the system. The communication system should minimize the power used at the remote units for the transport of data, as the equipment utilized at the remote units for transmission and reception may be supplied by power distributed over the transmission medium of the system.

Another problem arises from a fault in the system preventing communication between a head end and multiple remote units of a multi-point to point system. For example, a cut transmission line from a head end to many remote units may leave many users without service. After the fault is corrected, it is important to bring as many remote units back into service as quickly as possible.

Data integrity must also be addressed. Both internal and external interference can degrade the communication. Internal interference exists between data signals being transported over the system. That is, transported data signals over a common communication link may experience interference there between, decreasing the integrity of the data. Ingress from external sources can also effect the integrity of data transmissions. A telephony communication network is susceptible to "noise" generated by external sources, such as HAM radio. Because such noise can be intermittent and vary in intensity, a method of transporting data over the system should correct or avoid the presence of such ingress.

These problems, and others as will become apparent from the description to follow, present a need for an enhanced communication system. Moreover, once the enhanced system is described, a number of practical problems in its physical realization are presented and overcome.

Another embodiment provides a method and apparatus for a fast Fourier transform (FFT). This invention relates to the field of electronic communication systems, and more specifically to an improved method and apparatus for providing an FFT.

There are many advanced digital signal-processing applications requiring analysis of large quantities of data in short time periods, especially where there is interest in providing "real time" results. Such applications include signal processing in modems which use OFDM (orthogonal frequency division multiplexing). In order to be useful in these and other applications, Discrete Fourier Transform (DFT) or FFT signal processors must accommodate large numbers of transforms, or amounts of data, in very short processing times, often called high data throughput.

In addition to the speed and data-throughput requirements, power consumption is a major concern for many applications. In some signal-processing applications, power is supplied by portable generation or storage equipment, such as batteries, where the ultimate power available is limited by many environment. In such applications, processor power consumption must be as low as possible. One useful measure of utility or merit for FFT processors is the energy dissipation per transform point. Ultimately, one key problem with any FFT processor is the amount of power consumed per transform. Generally, high-performance, efficient FFT processors exhibit energy dissipations per transform in the range of 100 to 1000 times log.sub.2N nanojoules, where N is the number of points in a given transform. As a consequence, reasonably large transforms required to process large arrays of data, result in large power consumption.

Machine-implemented computation of an FFT is often simplified by cascading together a series of simple multiply-and-add stages. When a recursive process is used, data circulates through a single stage and the computational structure of the stage is made variable for each circulation. Each circulation through the stage is referred to as a "pass."

A plurality of computational elements, each known as a radix-r butterfly, may be assembled to define a single stage for carrying out a particular pass. A radix-r butterfly receives r input signals and produces a corresponding number of r output signals, where each output signal is the weighted sum of the r input signals. The radix number, r, in essence, defines the number of input components which contribute to each output component.

By way of example, a radix-2 butterfly receives two input signals and produces two output signals. Each output signal is the weighted sum of the two input signals. A radix-4 butterfly receives four input signals and produces four corresponding output signals. Each output signal of the radix-4 butterfly constitutes a weighted sum of the four input signals.

Completion of an N-point FFT requires that the product of the butterfly radix values, taken over the total number of stages or passes, equals the total point count, N. Thus, a 64-point FFT can be performed by one radix-64 butterfly, or three cascaded stages where each stage has sixteen radix-4 butterflies (the product of the radix values for stage-1 and stage-2 and stage-3 is 4.times.4.times.4=64), or six cascaded stages where each of the six stages comprises 32 radix-2 butterflies (the product of the radix values for stage-1 through stage-6 is 2.times.2.times.2.times.2.times.2.times.2=64).

A multi-stage or multi-pass FFT process can be correctly carried out under conditions where the number of butterfly elements changes from one pass (or stage) to the next and the radix value, r, of the butterfly elements also changes from one pass (or stage) to the next. A paper by Gordon DeMuth, "ALGORITHMS FOR DEFINING MIXED RADIX FFT FLOW GRAPHS," IEEE Transactions on Acoustics, Speech, and Signal Processing, Vol. 37, No. 9, September 1989, Pages 1349-1358, describes a generalized method for performing an FFT with a mixed-radix system. A mixed-radix system is one where the radix value, r, in one stage or pass is different from that of at least one other stage or pass.

An advantage of a mixed-radix computing system is that it can be "tuned" to optimize the signal-to-noise ratio of the transform (or more correctly speaking, to minimize the accumulated round-off error of the total transform) for each particular set of circumstances. By way of example, it is advantageous in one environment to perform a 512-point FFT using the mixed-radix sequence: 4, 4, 4, 4, 2. In a different environment, it may be more advantageous to use the mixed-radix sequence: 4, 2, 4, 4, 4. Round-off error varies within a machine of finite precision as a function of radix value and the peak signal magnitudes that develop in each stage or pass.

In addition, it may be advantageous to scale intermediate results between each stage or pass, in order to minimize round-off errors and the problem of overflow. Further, it may be advantageous to vary the amount of scaling performed between each pass, for example, either to scale by 1/4 between each radix-4 stage or to scale by 1/2 for some stages and 1/8 for other stages.

Heretofore, FFT processors generally fetched data values from their working storage in a serial manner, thus limiting the speed which could be obtained. Further, current FFT processors generally were limited in speed by loading the working storage with input values, then processing the data in the working storage, then unloading the result values.

There are many advanced digital signal-processing applications requiring analysis of large quantities of data in short time periods, especially where there is interest in providing "real time" results. Such applications include signal processing in modems which use OFDM (orthogonal frequency division multiplexing).

One need in the art is for an accurate analog-to-digital conversion (ADC) at moderate frequencies having limited bandwidth. One technology known in the art is the "Sigma-Delta" ADC which provides very good resolution (high number of bits in the digital re