Title of Invention

ACCESS SYSTEMS BASED ON THE OFDM TRANSMISSION TECHNIQUE

Abstract ABSTRACT The present invention relates to a new power-efficient multi-user indoor wireless method and system based on the OFDM transmission technique on the downlink. In the new system subcarrier and modulation mode are allocated such that the bit-rate and bit-error rate requirements of all the active users are simultaneously satisfied. Such a system is expected to be valuable in wireless multimedia communications where high-speed downlink access is extremely important. Power and bandwidth are two valuable resources in communications and the new system allocates these resources in an efficient manner. At present there are no schemes which have been presented to allocate resources in such an efficient manner while taking care of the user requirements. Results presented using simulations clearly illustrate the performance advantages of the new scheme when compared with other schemes.
Full Text FIELD OF TECHNOLOGY
This invention relates to the field of Wireless Data Communications. More particularly, this invention relates to a Multi-user Indoor Wireless Access Method and System based on the Orthogonal Frequency Division Multiplexing transmission technique. The envisaged application is the high bit-rate downlink of indoor wireless access systems.
DESCRIPTION OF PRIOR ART
Most high-speed indoor wireless access systems are based on the Orthogonal Frequency Division Multiplexing (OFDM) transmission technique due to its various advantages. In a multi-user indoor wireless access system, the downlink is considered to be the more crucial and important link, as there will be a requirement for high data rates in such an application. Typically internet access is a target application wherein more data is expected to come in the downlink rather than in the uplink. In wireless communications, spectrum or frequency is a key resource which needs efficient and careful allocation so that user requirements are met. The allocation problem becomes crucial as users of wireless systems demand more data rates; typically the situation wherein most of the internet access is through wireless might not be a far-fetched idea. Moreover, in wireless data applications, user requirements can be asymmetric and consequently intelligent and efficient resource (frequency, power) allocation techniques are needed to achieve high-capacity systems. Also, radiated power is an important factor as more wireless systems are used in the field.
Focus of this invention is on OFDM systems, which have been found to be suitable for high data-rate transmission in wireless environments. Methods such as 'adaptive modulation and multiple access for the OFDM transmission technique' and 'multi¬user OFDM with adaptive subcarrier, bit and power allocation' have been presented wherein approaches, which can be used to allocate subcarriers in an OFDM based multi-user system are detailed. A formulation has been presented to calculate the

analytical solution in a multi-user system so as to optimize power transmitted from the base station in the method for multiuser OFDM with adaptive subcarrier, bit and power allocation. Here, global channel knowledge is used to allocate subcarriers and modulation mode for the various users in the downlink transmission. Schemes have also been outlined in the adaptive modulation and multiple access for the OFDM transmission technique for subcarrier and modulation mode allocation. In this proposal fixed frequency resources are assigned to the users and modulation mode is varied. Various ways are outlined for allocating the resources considering the user requirements in the method for 'transmit optimization for OFDM/SDMA-based WLAN'. A thorough analysis of the allocation problem is carried out in the method for 'transmit power adaptation for multiuser OFDM systems' and it has been shown that subcarrier sharing results in interference problems. The authors propose allocating subcarriers to the strongest user and then equally distributing the power among the different subcarriers. The focus is on maximizing the net data rate as seen from all the users. It is noted that as the number of users increase, the net data rate exceeds the conventional channel capacity limits.
LIMITATIONS
There are no existing systems which have considered the allocation of subcamers and modulation mode in a joint manner for an OFDM based multiuser system such that the total power transmitted is minimized. Such a system is important in wireless communications where radiated power has to be kept low while satisfying user requirements. In the method for multiuser OFDM with adaptive subcarrier, bit and power allocation, a formulation is presented to calculate the analytical soluUon in a multi-user system so as to optimize power transmitted from the base station. The analytical solution is not realizable as it involves sharing of the subcarriers which is not feasible. Schemes have been outlined in the adaptive modulation and multiple access for the OFDM transmission technique for subcarrier and modulation mode allocation. However, the method presented does not consider the BER and BR requirements of the various users. It allocates fixed resources to the various resources. In practice, it is expected that the user requirements (in terms of the BER and BR) will be different. Schemes have been described in the method for 'transmit

optimization for OFDM/SDMA-based WLAN for subcarrier allocation exploiting the channel conditions. Specifically, the Fonward subcarrier allocation algorithm in which allocation is done to the user who is most benefited by the best subcarrier and the Backward subcarrier allocation algorithm in which allocation is done to the user who is least affected by the worst subcarrier have been mentioned. However, the outlined schemes do not consider optimising any transmitter resource (Power, BR, or BER), In the method for 'transmit power adaptation for multiuser OFDM systems', a system is proposed wherein frequency resources are allocated to users whose channel gains are the best for that particular subcarrier and power is equally distributed to all the subcarriers. This proposal does not address the allocation problem with the transmitted power in perspective; it is designed to achieve rate maximization with no constraints to satisfy.
OBJECTS OF THE INVENTION
It is the primary object of invention to invent multi-user indoor wireless access system and method based on the OFDM transmission technique, which is unique.
It is another object of the invention to invent a novel power efficient OFDM based multiple access system suitable for high bit-rate communications between a central base station and several terminals operating at the same time.
It is another object of the invention to design a novel system and method to allocate power and modulation mode such that the user requirements are satisfied.
It is another object of invention to invent a multi-user indoor wireless access system and method based on the OFDM transmission system, ensures the bit-rate requirements of the users in the system.
It is another object of invention to invent a multi-user indoor wireless access system and method based on the OFDM transmission system, which allocates frequency resources and modulation mode to the users such that the power transmitted is lesser than existing systems for similar applications.

SUMMARY OF THE INVENTION
The present invention proposes a new multi-user indoor wireless access system and method based on the OFDM transmission technique, which is unique and overcomes all the limitations mentioned above and addresses all the objectives mentioned above.
The present invention further proposes the multi-user indoor wireless access system and method based on the OFDM transmission technique for transmitting information in a high-speed indoor wireless access application. The application considered is illustrated in Figure 1, where a central base station is transmitting information to several portable users. It is assumed that there are 'K users in our system and each user has their own bit rate requirements.
The following description explains the salient features of the invention.
The new system and method improves upon other known systems for transmitting infonnation in such an application. The features of the new system and method are:
It ensures the BR and BER requirements of the users;
It allocates frequency resources and modulation mode to the users such that the
power transmitted is lesser than existing systems for similar applications.
The proposed system and method ensures minimal radiated transmit power while ensuring that all user rate constraints are met. This criterion is important as wireless users might have unequal and asymmetric data rate requirements at different times. This invention presents a power efficient system which will take user requirements into account and such an allocation scheme is expected to be of considerable value in the field of multimedia wireless communications.

Accordingly, the present invention comprises a multi-user indoor wireless access method based on the Orthogonal Frequency Division Multiplexing transmission technique comprising:
(a) allocation of sub-carrier to various users based on user requirements
and channel conditions comprising sub-carrier allocation method with
find(v, w) pair which has the minimum P as given by
^Pn.k - ~2 where P is the incremental power and v, w
refer to the subcarrier and user indices, respectively;
(b) allocation by modulation mode such that the requirements of all active
users are simultaneously met comprising following steps:
if the subcarrier v is already allocated to user w OR not allocated to any other user AND if the BR requirement is not satisfied, given mathematically as,
IF(<. or z> allocate one bit to the user w in the subcarrier v and increment the
power by ^v,«, wherein mathematically,
«/., = 1
/"is calculated using (19) and Find (v,w) = arg{min(A/')};
'v.w t'.w
P..,.=Pv.>, +AA.,.
U l^
c„ ,„ = c + 1
c) optimization of power at the transmitter such that the requirements of
all active users are met;
d) adopting adaptive modulation for the various subcarriers; and
e) allocation to accommodate different bit-rate and bit-error rate
requirements from the different users.

Accordingly, the present invention further comprises a multi-user indoor wireless access system based on ttie OFDM transmission technique inter alia comprising:
(a) a base station which is connected to multiple users and the downlink is effected through OFDM;
(b) a transmitter system which, inter alia, comprises an allocation scheme module, a modulation block module and an OFDM transmitter module; and
(c) a receiver system which comprises at least an OFDM receiver module connected lo an adaptive demodulation block.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates the OFDM based multiple access system for downlink communications.
Figure 2 illustrates the OFDM Time-Frequency grid.
Figure 3 shows the channel response in the frequency domain for two users.
Figure 4 shows the flow chart of the allocation scheme.
Figure 5 is the block diagram of the base station transmitter.
Figure 6 is the block diagram of the terminal's receiver.
Figure 7 shows the performance of the schemes in the equal PDP channel.
Figure 8 shows the performance of the schemes in the exponential PDP channel.
Figure 9 is the block diagram of operation of Transmitter System.

DETAILED DESCRIPTION OF THE INVENTION
The Orthogonal Frequency Division multiplexing (OFDM) transmission technique is used for communications between the base station (BS) and the terminals. This technique has become popular recently for providing high data rate multimedia services over severe multi path channels. In such channels, transmission of high data rate signals using conventional single carrier techniques can result in severe Inter Symbol Interference (ISI) and a consequent increase in the equalizer complexity. In such environments, OFDM systems offer low-complexity solutions and several new standards have adopted this technique. OFDM is a multi-carrier transmission scheme. It transmits data in parallel through several subcarriers. It also offers flexibility in multiple access by suitably dividing it among several users.
In one OFDM symbol, the data is modulated using 'N' subcarriers and when there are multiple users, each user may be allotted a set of subcarriers, i.e., the transmission of the data to a particular user can take place using the allotted set of subcarriers. This is illustrated using the OFDM Time-Frequency Grid shown in Figure 2.
MOTIVATION FOR ADAPTIVE ALLOCATION AND MODULATION
In a multi-user system, the channel response from the base station to each of the users is different. Also, the channel response among the different subcarriers for a single user may differ because of the frequency-selective nature of the multipath transmission channel and the large bandwidth of the system. In Figure 3, the channel response in the frequency domain for the 2-user case is shown.
Hence, depending on the channel response, the possible adaptations are Adaptively allocate the subcarriers to the users; Adaptively select the modulation mode among the allocated subcarriers.

We consider only the downlink of the multiple access system as it is expected that the requirements for the downlink will be challenging in terms of data rates. The uplink transmission can be based on any of the standard multiple access techniques.
ALLOCATION OF SUBCARRIERS, MODULATION MODE AND POWER
A method is outlined to assign subcarriers, modulation type, and power to each user depending on the channel conditions and requirements of all users. The basic philosophy of the method is as follows: In OFDM systems using adaptive modulation the modulation type employed on each subcarrier is different depending on the individual channel Signal to Noise Ratio (SNRs). Hence, the number of Bits Per Modulation Symbol (BPMS) transmitted in individual subcarriers are different based on the modulation type. The transmitted power needed to achieve a certain BER is different for the various modulation types. Hence, the power difference in transmitting x+1 and x BPMS on a subcarrier for a certain user can be calculated. Consider the condition wherein a certain subcarrier has been assigned to a user and it has been assigned x BPMS for transmission in the subcarrier. In this algorithm, we allocate an extra bit to that subcarrier vi/hich requires the least power to transmit one extra bit. Here Quadrature Amplitude Modulation (QAM) with square signal constellation is considered and the function f„(c) denotes the required received power level for reliable transmission of c BPMS and is given by
where.
EXPLANATION OF THE METHOD
The method works as follows:

Let ^ Pn.t for n^1....N and k=l..K, be an W x K matrix whose elements contain the transmit power required to transmit the specified modulation type in the corresponding subcarrier for all the users. Let Mc be the maximum number of subcarriers that can be allocated to any user. It is given by,
Mc = floor(N/K) (3)
Let f^«,* represent the number of BPMS used and '",* is a variable used to keep track of the current constellation size for computational purposes.
Initialization:
Let '..» 0 P., 0 c„, 0
P P.M for all n=t-,/V and/(=!,,.Awhere
An be the incremental energy required to transmit additional bit in the n'^ subcarrier of the k'*^ user and is given by
^Pn,,= —2 (4)

lh
Let Bi, denote the number of bits to be transmitted in one OFDM symbol for the k
user.
VERBAL DESCRIPTION OF THE ALLOCATION SCHEME
Consider an W x / Ai-
and ^l.j 1, if the /"' subcarrier is allocated to the/" user
^^u ", otherwise 1- Find
2. If 2-^^',- = ^" then remove the user w from further iterations by making
1=1
/'"."■ for all n=1,....,N, else
3. If the number of subcarriers allocated to the user w is equal to Mc i.e.
Zi'^^j.^^^^c, then within the allocated subcarriers for the user w perform single
user optimum bit allocation to satisfy the user's BR requirement given by {3) and
remove the user ivfrom further iterations by making P".^ for all n=1,....,N, else
4. If the subcarrier v is already allocated to user w OR not allocated to any other
user AND if the BR requirement is not satisfied. Mathematically.
K ,V
IF ( allocate one bit to the user w in the subcarrier v and increment the power by P>>.
Mathematically,
<..> P.,.=P...+^Pr..
calculate P using (19) and go to step 1
5. If the subcarrier v is allocated to the user '^ ^i.e. {'^v,. 0 ^ND
K
Z
After the algorithm has converged^ K.^} gj^gs the number of BPMS to be
transmitted and ^ P..k gives the corresponding transmit power required to achieve this.
FLOW CHART OF THE ALLOCATION SCHEME
The flow chart for the allocation scheme is represented in Figure 4.
After the allocation method finishes, Cn,h gives the number of bits to be transmitted in the nth subcarrier of the ^('^ subcarrier and Pn,/ TRANSMITTER SYSTEM
The transmitter contains 2 blocks as shown in Figure 5. The allocation method outlined in the previous section is used to calculate the subcarrier, modulation mode and power to the subcarriers. The information about the channel conditions can be obtained using vahous methods. The QOS requirements of the users in terms of BER and BR for each user have to be supplied. The allocation block will then supply the resource allocation output to the OFDM transmitter section. The bits for the intended users are then modulated accordingly by using the modulation mode and subcarrier allocation information and are transmitted through an antenna. A control channel is used to transmit the allocation information to all the users. The allocation can be repeated after any number of OFDM symbols depending on the changes in the environment and user requirements.
The transmitter in the downlink does the combined subcarrier and modulation mode allocation as shown in figure 9 using the following steps:
• The channel information of all users is obtained by the base station transmitter by sending 2 Pilot OFDM symbols in every frame.
• In addition, the base station transmitter also specifies the users to whom data is to be sent in the following frame.

• The active users who are listening to the radio transmissions from the base
station report back the channel status in pre-assigned time slots at the end of
the frame.
• Based on the number of users who have responded and the channel state
.information reported by the respective users, the base station transmitter
assigns the subcarrier and modulation mode so as to minimize the transmit power as outlined in the method.
The operations that need to be completed at the base station transmitter system are outlined in the steps and flowcharts given. The mathematical operations that are used in the system are additions and multiplications. In our system, a general purpose microprocessor shall be programmed with these equations and the output is the allocation information for the following frame. This information is supplied to the control processor of the base station which uses this information to select number of bits in each user stream and to route it to the correct subcarrier.
RECEIVER SYSTEM
The receiver for the m*^ terminal (in general, it could be any one of the K terminals) contains an antenna and an OFDM receiver block as shown in figure 6. The output of the OFDM receiver block is sent to an adaptive demodulator. The adaptive demodulator uses the control channel information about the allocation of the subcarriers and the modulation mode to demodulate the information in the subcarriers, which were allocated for transmitting its signal.
PERFORMANCE ADVANTAGES OF THE PROPOSED SCHEME
We have compared the performance of the new scheme with other multiple access schemes. Shown below are the BER Vs Eb/No curves for the different schemes under different channel conditions. These curves clearly elucidate the advantages of the new scheme. We gain around 3 dB by using the new allocation algorithm compared to the OFDM - TDt\/lA scheme. The proposed scheme for minimizing the

total transmit power can be easily modified to achieve the maximum throughput when the transmit power is l Simulation parameters

Number of subcarhers, N
Number of Users, K
Subcarrier spacing, fd
Sampling Rate, fs

128 10
39.062500 kHz 5.000000 MHz



Ts
Symbol time,
Length of cyclic prefix, L Number of taps
Total bit rate

27.600000 us
10
5
18.550725 MBPS

The systems simulated are
New proposed system
OFDM TDMA system
OFDM Interleaved FDMA system[5].
The performance of the system is evaluated under two different types of channels
Equal PDP channel
Exponential PDP channel as shown in figures 7 and 8
The foregoing description of a preferred embodiment of the invention has been presented for the purpose of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious

modifications or variations are possible in light of the above teachings.
Although the invention has been described with respect to specific embodiments thereof, these embodiments are merely illustrative, and not restrictive of the invention.
In the description herein, numerous specific details are provided, such as examples of components and/or methods, to provide a thorough understanding of embodiments of the present invention. One skilled in the relevant art will recognize, hovi/ever, that an embodiment of the invention can be practiced without one or more of the specific details, or with other apparatus, systems, assemblies, methods, components, materials, parts, and/or the like. In other instances, well-known structures, materials, or operations are not specifically shown or described in detail to avoid obscuring aspects of embodiments of the present invention.
A "processor" or "process" includes any human, hardware and/or software system, mechanism or component that processes data, signals or other information. A processor can include a system with a general-purpose central processing unit, multiple processing units, dedicated circuitry for achieving functionality, or other systems. Processing need not be limited to a geographic location, or have temporal limitations. For example, a processor can perform its functions in "real time," "offline," in a "batch mode," etc Portions of processing can be performed at different times and at different locations, by different (or the same) processing systems.
A "computer-readable medium" for purposes of embodiments of the present invention may be any medium that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, system or device. The computer readable medium can be, by way of example only but not by limitation, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, system, device, propagation medium, or computer memory.

Embodiments of the invention may be implemented by using a programmed general purpose digital computer, by using application specific integrated circuits, programmable logic devices, field programmable gate arrays, optical, chemical, biological, quantum or nano-engineered systems, components and mechanisms may be used. In general, the functions of the present invention can be achieved by any means as Is known in the art. Distributed or networked systems, components and circuits can be used. Communication, or transfer, of data may be wired, wireless, or by any other means.
It will also be appreciated that one or more of the elements depicted in the drawings/figures can also be implemented in a more separated or integrated manner, or even removed or rendered as inoperable in certain cases, as is useful in accordance with a particular application. It is also within the spirit and scope of the present invention to implement a program or code that can be stored in a machine-readable medium to permit a computer to perform any of the methods described above.
Additionally, any signal arrows in the drawings/Figures should be considered only as exemplary, and not limiting, unless otherwise specifically noted. Furthermore, the term "or" as used herein is generally intended to mean "and/or" unless otherwise indicated. Combinations of components or steps will also be considered as being noted, where terminology is foreseen as rendering the ability to separate or combine is unclear.
As used in the description herein and throughout the claims that follow, "a", "an", and "the" includes plural references unless the context clearly dictates othenivise. Also, as used in the description herein and throughout the claims that follow, the meaning of "in" includes "in" and "on" unless the context clearly dictates otherwise.
The foregoing description of illustrated embodiments of the present invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed herein. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes only.

various equivalent modifications are possible within the spirit and scope of the present invention, as those sl Thus, while the present invention has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended in the foregoing disclosures, and it wilt be appreciated that in some instances some features of embodiments of the invention will be employed without a corresponding use of other features without departing from the scope and spirit of the invention as set forth. Therefore, many modifications may be made to adapt a particular situation or material to the essential scope and spirit of the present invention. It is intended that the invention not be limited to the particular terms used in following claims and/or to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include any and all embodiments and equivalents falling within the scope of the appended claims.

REFERENCES
1. Leonard J.Cimini, JR. "Performance studies for high-speed indoor wireless communications," Wireless Personal Communications, no. 2, pp. 67-85,1995.
2. 2, Wang and G. B. Giannakis, "Wireless Multicarrier Communications: Where Fourier Meets Shannon" IEEE Signal Processing Magazine, vol. 17, no. 3. pp. 29-48, May 2000,
3. S. Thoen, Transmit Optimization for OFDM/SDMA-based Wireless Local Area Netwof1 4. ETS 300 744 Ver 0,0.3, "Digital broadcasting systems for television, sound and data services; Framing structure, channel coding and modulation for digital terrestrial television", ETSI -European Telecommunications Standards Institute.
5. Rainer Grunhetd and Hermann Rohling, "Adaptive modulation and multiple access for the OFDM transmission technique," Wireless Personal Communications, no. 13, pp. 5-13, 2000.
6. L.Hanzo, W.Webb and T.Keller, "Single and multicarrier quadrature amplitude modulation," 1^' Ed., John Wiley & Sons, 2000.
7. John M.Cioffi, "A multicarrier primer", http://www-isl.stanford.edu/people/cioffi/pdf/multicarrier.pdf
8. Cheong Yui Wong, Roger S.Cheng, Khaled Ben Letaif and Ross D.Murch, "Multiuser OFDM with adaptive subcarrier, bit and power allocation," IEEE Journal on selected areas in communications, vol. 17, no. 10, pp. 1747-1758, October1999.

9. J. G. Proakis, Digital Communications, 3"" Ed. New York: McGraw Hill, 1995. Sara Baase and Allen Van Gelder, Computer Algorithms: Introduction to design and analysis, 3"^ Ed., Addison Wesley. 2000
10. Kenneth H.Rosen, Discrete mathematics and its applications, 4"^ Ed., McGraw-Hill, 1999.
11. Kaveh Pahlavan and Allen H. Levesque, Wireless information networks. John Wiley & Sons, Inc., 1995.
12. J. Jang and K. B. Lee, "Transmit power adaptation for multiuser OFDM systems", IEEE Journal on Selected Areas in Communications, pp. 171-178, vol.21, no. 2, Feb. 2003.


WE CLAIM
1. A multi-user indoor wireless access method based on the Orthogonal Frequency Division Multiplexing (OFDM) transmission technique comprising:
(a) allocation of sub-carrier to various users based on user requirements and channel conditions comprising sub-carrier allocation method with find(v, w) pair which has the minimum P as given by

(c) optimization of power at the transmitter such that the requirements of all active users are met;
(d) adopting adaptive modulation for the various subcarriers; and
(e) allocation to accommodate different bit-rate and bit-error rate requirements from the different users.

2. The method as claimed in claim 1, wherein the adaptive modulation for the
various sub-carriers allocated to a user "w" is accomplished using the
following method:
if the number of subcarriers allocated to the user w is equal to M^ i.e.

3. The method as claimed in any of the preceding claims, which is capable of
accommodating users with varying bit-rate and bit-error rate requirements at
any given time.
4. A multi-user indoor wireless access system based on the OFDM transmission
technique inter alia comprising;
(a) a base station which is connected to multiple users and the downlink is
effected through OFDM;
(b) a transmitter system which, inter alia, comprises an allocation scheme
module, a modulation block module and an OFDM transmitter module; and
(c) a receiver system which comprises at least an OFDM receiver module
connected to an adaptive demodulation block.
5. The system as claimed in claim 4, wherein the said OFDM is a multi-carrier
transmission scheme where data is transmitted in parallel through several
subcarriers which offers flexibility in multiple access by suitably dividing the
said subcarriers among several users.
6. The system as claimed in claims 4 & 5, wherein depending on the channel
response, the adaptations adaptively allocate the subcarriers to the users and
adaptively select the modulation mode among the allocated subcarriers.

7. The system as claimed in claims 4 to 6, wherein in the said transmitter system the QOS requirements of the users in terms of BER and BR for each user have to be supplied and further the allocation block will supply the resource allocation output to the OFDM transmitter section.
8. The system as claimed in claims 4 to 7, wherein in the said transmitter system the bits for the intended users are modulated accordingly by using the modulation mode and subcarrier allocation information are transmitted through a means such as antenna.
9. The system as claimed in claims 4 to 8, wherein in the said transmitter system a control channel is used to transmit the allocation information to all the users and this allocation can be repeated after any number of OFDM symbols depending on the changes in the environment and user requirements.
10. The system as claimed in claims 4 to 9, wherein the said transmitter in the downlink does the combined subcarrier and modulation mode allocation.
11. The system as claimed In claims 4 to 10, wherein the channel information of any and / or all users is obtained by the base station transmitter by sending at least 2 Pilot OFDM symbols in every frame.

12. The system as claimed in claims 4 to 11, wherein the base station transmitter further specifies the users to whom data is to be sent in the following frame and the active users who are listening to the radio transmissions from the base station report back the channel status in pre-assigned time slots at the end of the frame.
13. The system as claimed in claims 4 to 12, wherein based on the number of users who have responded and the channel state information reported by the respective users, the base station transmitter assigns the subcarrier and modulation mode so as to minimize the transmit power.

14. The system as claimed in claims 4 to 13, wherein a general purpose microprocessor is programmed with the required mathematical equations and the output is the allocation information for the following frame which is supplied to the control processor of the base station which uses this information to select number of bits in each user stream and to route it to the correct subcarrier.
15. The system as claimed in claims 4 to 14, wherein in the receiver system the output of the OFDM receiver block is sent to an adaptive demodulator and the adaptive demodulator uses the control channel information about the allocation of the subcarriers and the modulation mode to demodulate the information in the subcarriers, which were allocated for transmitting its signal.
16. A multi-user indoor wireless access system based on the OFDM transmission technique in which the method as claimed in claims 1 to 3 is implemented.
17. A multi-user indoor wireless access method based on the OFDM transmission technique as claimed in the preceding claims and as substantially described and illustrated herein.
18. A multi-user indoor wireless access system based on the OFDM transmission technique as claimed in the preceding claims and as substantially described and illustrated herein.



Documents:

0320-mas-2002 abstract-duplicate.pdf

0320-mas-2002 abstract.pdf

0320-mas-2002 assignment.pdf

0320-mas-2002 claims-duplicate.pdf

0320-mas-2002 claims.pdf

0320-mas-2002 correspondence-others.pdf

0320-mas-2002 correspondence-po.pdf

0320-mas-2002 description (complete)-dup.pdf

0320-mas-2002 description (complete)-org.pdf

0320-mas-2002 drawings-duplicate.pdf

0320-mas-2002 drawings.pdf

0320-mas-2002 form-1.pdf

0320-mas-2002 form-19.pdf

0320-mas-2002 form-4.pdf


Patent Number 198873
Indian Patent Application Number 320/MAS/2002
PG Journal Number 30/2009
Publication Date 24-Jul-2009
Grant Date
Date of Filing 26-Apr-2002
Name of Patentee THE ANNA UNIVERSITY
Applicant Address CHENNAI, INDIA
Inventors:
# Inventor's Name Inventor's Address
1 RAJENDRAN VENKATESH THE ANNA UNIVERSITY, CHENNAI, INDIA
2 KARTHIKEYAN SUNDARESAN THE ANNA UNIVERSITY, CHENNAI, INDIA
3 PATCHAI ARUN THE ANNA UNIVERSITY, CHENNAI, INDIA
4 SUBRAMANIAN SRIKANTH THE ANNA UNIVERSITY, CHENNAI, INDIA
PCT International Classification Number H04B10/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA