Difference between revisions of "Quality of Service on CDMA platforms"

Latest revision as of 23:37, 5 August 2009

Cellular communication

In the next sections we discuss the basics for the Patents EP1385290 and EP1156616.

Quality of Service(QoS)

CDMA is being accepted as a third generation (3G) system and a specific feature of 3G systems is that they offer a radio interface adapted for all kinds of services and combination of services (such as data, voice, video etc). The big challenge is multiplexing these services which do not have the same demands in terms of quality of service(QoS) which can be represented as BER(bit error rate), processing delay, frame error rate etc. Different QoS will require different channel encoding and interleaving strategies. The demand of BER can be satisfied when the coding bits have at least a code dependent ratio Eb/I(ratio of bit energy to interference).

Need for Rate Matching

In a system using Multiple Access CDMA technology, the greater the Eb/I ratio the greater is the QoS. Transport channels having different QoS requirement do not have the same need in terms of Eb/I ratio. If all the channels are allocated a fixed Eb/I ratio which corresponds with the maximum required by a transport channel then other channels will have "too" good a Quality of Service, needlessly causing interference and resource blocking. There are several influences that might change system performance(BER) and hence Eb/I ratio,in accordance with the required QoS of which the most effective is variation of Bit Rate by a step of Rate Matching. The standard framework for the management of QoS in CDMA systems is shown below. The following framework highlights the various steps involved in providing variable QoS. The received data from the transport block is classified into different processes based on their QoS. Data is split onto various transport channels to which a CRC code is attached for error correction. Further, all these transport channels are multiplexed on one line by concatenation, interleaved, segmented and then rate matched. The rate matching step is performed using the rate matching ratio and puncturing ratio which is received from the sending entity (an exchange of handshaking signals occurs).

QoS Management in CDMA - Standard Framework

The rate matching step in above figure is essentially implemented by repetition or puncturing, SIEMENS has proposed an algorithm to ETSI, to obtain a non-integer punture/repetition ratio referenced SM/G2/UMTS-L1/Tdoc428/98 and it is given as follows. This algorithm is used as a standard approach for Rate Matching.

Rate matching algorithm by SEIMENS

CDMA Basics

CDMA basics

QoS Management Algorithms

Quality of Service can be managed according to the varying type of traffic i.e. data, voice, video in the following four ways.

Rate Matching Algorithm
Code Hopping Algorithm
Dynamic Resource Scheduling(DRS) Algorithm
Optimal Power Control Algorithm

QoS Management in CDMA - Analysis restricted till 1999

Rate Matching Algorithm

The patent EP1385290 titled "Method for balancing Eb/I ratio in a service multiplexing CDMA system and a telecommunication system using this method" targets this concept of Rate matching and introduces an algorithm for calculating effective data output bits by a process of repetition or puncturing of the input bits governed by a rate matching ratio and puncturing ratio received from the sending entity (can be a BS or MS). As the number of services increases the number of potential combinations will also increase. There arises a need for simple arithmetic procedures to calculate the transport sizes which is done using the following three rules.

The first rule concerns Channel encoding wherin the transport block is converted into the coded block by a possible relation of the form Y=X/(coding rate)+Ntail
The second rule concerns segmentation of the coded block into the size of the segment produced by segmentation per multiplexing frame
The third rule is about obtaining the size of the oputput block Y from the Input block X according to a rate matching step explained below.

The Parameters Ei(Energy per bit),Pi(Max puncture Rate) and Xi(Input data rate) are the characteristic constants of a transport channel both at the Mobile Station(MS) and the Base Station(BS). Initially Ei,Pi and Xi are determined at the Base Station and a maximum possible payload is calculated. This is known as the intermediate size and and a vector of expected is transmitted to the Mobile Station(MS) along with the parameters Ei and Pi. Using the values of Pi,Ei and Xi the mobile will also calculate its output frame size Yi. Then final step is matching this value of Yi with the received vector of Intermediate values Yi and decide the final frame size. The bits are repeated or punctured according to the required Final Frame Size.

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Code Hopping Algorithm

According to one of the methods of dynamic power control (Code Hopping) used in W-CDMA technology, the Rate Information (RI) field in the uplink control channel in W-CDMA frame can be used to notify the base station about the variable bit rates (VBR) it wants to send, then the base station assigns a new spreading factor for each data rate and hence the optimal power calculation is done according to the spreading factor as follows.
Spreading factor(Gi) is defined as the ratio of bandwidth of the system to the data rate of the radio frame. Mathematically,
Gi = W / Ri,where W=system bandwidth which is a constant for a system and Ri= data rate of radio frame.
A power index (gi) is calculated from this Spreading Factor(Gi) using the following expression
gi= (vi / (vi+Gi)), where vi is minimum QoS for the ith session which is a constant.
This power index will ascertain the optimal power to be alloted to each service channel(each data rate for different services).
Pi = (gi*No*W )/ (Hi*(1-(Sgj)
where No is AWGN(Additive White Guassian Noise)a constant,
Hi is path loss which is dependent on the distance and is a constant for a path,
and Sgj is sum of the power index of all the sessions which is constant for all sessions of the radio frame.

From the above analysis, we observe that when the mobile is sent the optimal power at which it should transmit. It can backtrack and calculate the power index and spreading factor and hence the Data rate is changed accordingly. This step can be considered to be an equivalent to the Rate Matching Algorithm explained above. The method and algorithm to schedule optimal power is detailed in the IEEE paper 765366 Dynamic Resource Scheduling for Variable QoS Traffic in W-CDMA - Ozgur Gurbuz, Henry Owen.

Thus, we conclude that by adjusting the optimal power we are actually trying to implement a rate matching step.

Dynamic Resource Scheduling(DRS) Algorithm

The Mobile Station(MS) performs Matching of Traffic Descriptors such as Peak Cell Rate(PRC),Sustainable Cell Rate(SCR) and obtains the connection parameters like average cell rate, SIR, Delay from them. These parameters are sent to the Base Station(BS) where they are queued in a FIFO. The BS determines a spreading factor which allocates the Orthogonal Varible Spread code(OVSF) using Gi = W / Ri,where W=system bandwidth which is a constant for a system and Ri= data rate of radio frame.
The base station calculates a value of power index gi= (vi / (vi+Gi))and hence Power levels using Pi = (gi*No*W )/ (Hi*(1-(Sgj)), where S stands for sumof, and transmits them to the MS. This information is conveyed to the MS using TPC(Transmission Power Control) bits and a closed loop power control method as explained in section 5.6 above is performed to obtain the final value of power at which transmission should be done.The method and algorithm to schedule optimal power using Dynamic Resource Scheduling is detailed in the IEEE paper 765366 Dynamic Resource Scheduling for Variable QoS Traffic in W-CDMA - Ozgur Gurbuz, Henry Owen.

Optimal Power Control Algorithm

The Base Station receives a Pilot Signal from the Mobile station and calculates BER based on Distance,Transmission rate and No of Users in the Cell. Ptk is the transmitted signal power which is expressed by the power control function g ( rt , k ), a function of the distance from the mobile to base station, Ptk= g(rt,k)Po where Po is the maximum transmission power. The optimum power functions are transmitted to the Mobile station which calculates the optimal power and starts transmitting at that value. Thus meeting the required QoS parameters.The method and algorithm for optimal power control is detailed in the IEEE paper 503476 Optimal power control law for Multi-media - Multi-rate CDMA systems - Shee Yao and Evaggelos Geraniotis .

Research Activity (Non Patent) in the Period (1991-2003)

NOTE: The analysis presented below is with respect to the IEEE Papers published between 1991-2003 which focus on the aspect of Quality of Service and its Management using various paramters like Rate matching, Power control, Variable Spreading Factor etc.

Number of publications VS Year of publication

The above analysis suggests a increase in the Research activity in the area of QoS Management in the year 1999.

Publisher VS number of publications during(1991-2003)

It is to be noted that the non patent research is attributed mostly to universities in USA and Asia Pacific. The mention of IEEE member in the above graph indicates the absence of information about the parent department of the Researcher.

Graph showing number of publications by the publishers during 1991-2003

Conclusion

Substantial amount of research has been done in the field of QoS in CDMA communication system in the year 1998-99 and this has led to the invention of multitude of methodologies ranging from power control to Rate matching and Dynamic Resource scheduling, all with the sole aim of improving QoS.

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@@ Line 1: / Line 1: @@
-==Cellular Communication==
+==Cellular communication==
-A cellular mobile communications system uses a large number of low-power wireless transmitters to create cells—the basic geographic service area of a wireless communications system. Variable power levels allow cells to be sized according to the subscriber density and demand within a particular region. As mobile users travel from cell to cell, their conversations are handed off between cells to maintain seamless service. Channels (frequencies) used in one cell can be reused in another cell some distance away. Cells can be added to accommodate growth, creating new cells in unserved areas or overlaying cells in existing areas.
+[[CDMA Basics]]
-[http://www.IEC.org Source]<br>
-There are three main entities in cellular communication
-* Mobile station (MS)- consists of 2 entities- Equipment and SIM card
-* Base Transceiver station(BTS) - consists of 2 entities- Base transceiver(transmitter and receiver) station and Base station controller. This is the antenna tower site.
-* Main Switching centre(MSC) - Heart of the network, Central switching office which controls all the base stations and provides connection with landline phones.
-Three main jobs:
-# connects calls from sender to receiver
-# collects details of the calls made and received
-# supervises operation of the rest of the network components
-==Cellular System Architecture==
+In the next sections we discuss the basics for the Patents EP1385290 and EP1156616.
-Increases in demand -  more users in their systems.Amount of frequency spectrum available for mobile cellular use was limited, efficient use of the required frequencies was needed for mobile cellular coverage. In modern cellular telephony, rural and urban regions are divided into areas according to specific provisioning guidelines. Provisioning for each region is planned according to an engineering plan that includes cells, clusters, frequency reuse, and handovers.
+==Quality of Service(QoS)==
+CDMA is being accepted as a third generation (3G) system and a specific feature of 3G systems is that they offer a radio interface adapted for all kinds of services and combination of services (such as data, voice, video etc). The big challenge is multiplexing these services which do not have the same demands in terms of quality of service(QoS) which can be represented as BER(bit error rate), processing delay, frame error rate etc. Different QoS will require different channel encoding and interleaving strategies. The demand of BER can be satisfied when the coding bits have at least a code dependent ratio Eb/I(ratio of bit energy to interference).
-'''Cells'''
+===Need for Rate Matching===
-A cell is the basic geographic unit of a cellular system. Cells are base stations transmitting over small geographic areas that are represented as hexagons.
+In a system using Multiple Access CDMA technology, the greater the Eb/I ratio the greater is the QoS. Transport channels having different QoS requirement do not have the same need in terms of Eb/I ratio. If all the channels are allocated a fixed Eb/I ratio which corresponds with the maximum required by a transport channel then other channels will have "too" good a Quality of Service, needlessly causing '''interference and resource blocking'''. There are several influences that might change system performance(BER) and hence Eb/I ratio,in accordance with the required QoS of which the most effective is variation of Bit Rate by a step of '''Rate Matching'''. The standard framework for the management of QoS in CDMA systems is shown below. The following framework highlights the various steps involved in providing variable QoS. The received data from the transport block is classified into different processes based on their QoS. Data is split onto various transport channels to which a CRC code is attached for error correction. Further, all these transport channels are multiplexed on one line by concatenation, interleaved, segmented and then rate matched. The rate matching step is performed using the rate matching ratio and puncturing ratio which is received from the sending entity (an exchange of handshaking signals occurs).<br>
+[[Image:cdma_2_7.jpg|thumb|700px|center|QoS Management in CDMA - Standard Framework]]
-'''Clusters'''
+The rate matching step in above figure is essentially implemented by repetition or puncturing, SIEMENS has proposed an algorithm to ETSI, to obtain a non-integer punture/repetition ratio referenced SM/G2/UMTS-L1/Tdoc428/98 and it is given as follows. This algorithm is used as a standard approach for Rate Matching.
-A cluster is a group of cells. No channels are reused within a cluster. Normally a cluster has seven-cells in it as shown below.
+[[Image:cdma21.jpg|thumb|700px|center|Rate matching algorithm by SEIMENS]]
-'''Frequency Reuse'''
+[[Image:Cdma1.JPG|thumb|center|700 px|CDMA Basics]]
-Number of radio channel frequencies are limited. The concept of frequency reuse is based on assigning to each cell a group of radio channels used within a small geographic area. Cells are assigned a group of channels that is completely different from neighboring cells. The coverage area of cells is called the footprint. This footprint is limited by a boundary so that the same group of channels can be used in different cells that are far enough away from each other so that their frequencies do not interfere.
-'''Cell Splitting'''
+[[Media:Cdma_talk.pdf|CDMA basics]]
-As a service area becomes full of users, this approach is used to split a single area into smaller ones. In this way, urban centers can be split into as many areas as necessary to provide acceptable service levels in heavy-traffic regions, while larger, less expensive cells can be used to cover remote rural regions
+===QoS Management Algorithms===
+Quality of Service can be managed according to the varying type of traffic i.e. data, voice, video in the following four ways.
+# Rate Matching Algorithm
+# Code Hopping Algorithm
+# Dynamic Resource Scheduling(DRS) Algorithm
+# Optimal Power Control Algorithm
+[[Image:cdma_22.jpg|thumb|600 px|center|QoS Management in CDMA - Analysis restricted till 1999]]
-'''Handoff'''
+===Rate Matching Algorithm===
+The patent [http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=EP1385290&F=0 EP1385290] titled "Method for balancing Eb/I ratio in a service multiplexing CDMA system and a telecommunication system using this method" targets this concept of Rate matching and introduces an algorithm for calculating effective data output bits by a process of repetition or puncturing of the input bits governed by a '''rate matching ratio''' and '''puncturing ratio''' received from the sending entity (can be a BS or MS). As the number of services increases the number of potential combinations will also increase. There arises a need for simple arithmetic procedures to calculate the transport sizes which is done using the following three rules.
+# The first rule concerns Channel encoding wherin the transport block  is converted into the coded block by a possible relation of the form Y=X/(coding rate)+Ntail
+# The second rule concerns segmentation of the coded block into the size of the segment produced by segmentation per multiplexing frame
+# The third rule is about obtaining the size of the oputput block Y from the Input block X according to a rate matching step explained below.<br>
+The Parameters Ei(Energy per bit),Pi(Max puncture Rate) and Xi(Input data rate) are the characteristic constants of a transport channel both at the Mobile Station(MS) and the Base Station(BS). Initially Ei,Pi and Xi are determined at the Base Station and a maximum possible payload is calculated. This is known as the intermediate size and and a vector of expected is transmitted to the Mobile Station(MS) along with the parameters Ei and Pi. Using the values of Pi,Ei and Xi the mobile will also calculate its output frame size Yi. Then final step is matching this value of Yi with the received vector of Intermediate values Yi and decide the final frame size. The bits are repeated or punctured according to the required Final Frame Size.<br>
-The final obstacle in the development of the cellular network involved the problem created when a mobile subscriber traveled from one cell to another during a call. As adjacent areas do not use the same radio channels, a call must either be dropped or transferred from one radio channel to another when a user crosses the line between adjacent cells. Because dropping the call is unacceptable, the process of handoff was created. Handoff occurs when the mobile telephone network automatically transfers a call from radio channel to radio channel as a mobile crosses adjacent cells
-==Evolution of Cellular Systems==
-[[Image:cdma1.jpg|500 px|center]]
-==Multiple Access Methods==
-There are predominantly three types of multiple access methods.<br>
-'''Frequency Division Multiple Access:''' In this system each user is alloted a different set of frequency to operate upon. The uplink(mobile to base station) frequency is different from downlink frequency(base station to mobile).
-[[Image:cdma6.jpg]]<br>
-[Ref:www.ai.u-hyogo.ac.jp/~thai-proj/presen/20051222-Ishikawa.ppt]
-'''Time Division Multiple Access:'''In this system each user is allocated a different time slot.Forward link frequency and reverse link frequency is the same. A synchronous switch is responsible to do the time switching.
-[[Image:cdma10.jpg]]
-'''Code Division Multiple Access:'''There is no restriction on time and frequency in this scheme. All the users can transmit at all times and at all frequencies. Because users are isolated by code, they can share the same carrier frequency, eliminating the frequency reuse problem encountered in other technologies.<br>
-[[Image:cdma11.jpg|600 px|centre]]<br>
-A comparative study between the above three access technologies with respect to time and frequency is as shown below<br>.
-[[Image:cdma12.jpg|600 px|centre]]
-==Code Division Multiple Access==
+===<span style="color:#C41E3A">Like this report?</span>===
-The CDMA technology can be implemented in two ways
+<p align="center"> '''This is only a sample report with brief analysis''' <br>
-* Direct Sequence Spread Sprectrum - DSSS CDMA
+'''Dolcera can provide a comprehensive report customized to your needs'''</p>
-* Frequency Hopping - FH CDMA
+{|border="2" cellspacing="0" cellpadding="4" align="center" "
-'''Direct Sequence Spread Sprectrum - DSSS CDMA:''' In this method the direct sequence(input data) which is spread over a limited bandwidth is multiplied with a code or spreading sequence (a pseudorandom sequence) which will spread the input data over the entire bandwidth of the communication channel. The power density is also reduced and is spread over the frequency spectrum and hence is known as spread spectrum method. The modulation part of DSSS is as shown below<br>
+|style="background:lightgrey" align = "center"  colspan = "3"|'''[mailto:info@dolcera.com <span style="color:#0047AB">Buy the customized report from Dolcera</span>]'''
-[[Image:cdma13.jpg]]
+|-
-The modulated signal is transmitted over the channel and all users can receive it but only the user which knows the correct code can only decode the message. This is depicted in the figure below.<br>
+| align = "center"| [http://www.dolcera.com/website_prod/services/ip-patent-analytics-services Patent Analytics Services]
-[[Image:cdma14.jpg]]
+|align = "center"| [http://www.dolcera.com/website_prod/services/business-research-services Market Research Services]
-===Features of CDMA===
+|align = "center"| [http://www.dolcera.com/website_prod/tools/patent-dashboard Purchase Patent Dashboard]
-====Frequency Reuse====
+|-
-Number of radio channel frequencies are limited. The concept of frequency reuse is based on assigning to each cell a group of radio channels used within a small geographic area. Cells are assigned a group of channels that is completely different from neighboring cells. The coverage area of cells is called the footprint. This footprint is limited by a boundary so that the same group of channels can be used in different cells that are far enough away from each other so that their frequencies do not interfere.
+|align = "center"| [http://www.dolcera.com/website_prod/services/ip-patent-analytics-services/patent-search/patent-landscapes Patent Landscape Services]
+|align = "center"| [http://www.dolcera.com/website_prod/research-processes Dolcera Processes]
-====Soft Handoff==== Handoff means Switching a cellular phone transmission from one cell to another as a mobile user moves into a new cellular area.  It is so called because the radio link with the previous sector(s) is not broken before a link is established with a new sector; this type of handoff is described as "make before break". In CDMA due to this soft handoff there is no interruption of call even at the border of cell site which means more number of customers can be accommodated automatically increasing the capacity of the cell site.
+|align = "center"| [http://www.dolcera.com/website_prod/industries Industry Focus]
+|-
-====Multipath Fading==== In a mobile environment a mobile station will receive one direct signal from the base station and multiple signals which are reflected from obstructions like building and towers. Each signal would have travelled a different length and would be displaced in time. Due to this when they are combined at the mobile it will cause interference resulting in poor signal quality. This is called as fading. This problem is handled in a very good way in CDMA. Here the phase of the multiple signals is modified such the only positive interference(addition) takes place the overall signal strength increases. A receiver that implements the above principle is known as a RAKE receiver as shown in the figure below<br>
+|align = "center"| [http://www.dolcera.com/website_prod/services/ip-patent-analytics-services/patent-search/patent-landscapes Patent Search Services]
-[[Image:cdma15.jpg]]
+|align = "center"| [http://www.dolcera.com/website_prod/services/ip-patent-analytics-services/alerts-and-updates Patent Alerting Services]
-====Near Far Problem====  The problem is described by taking an example consider a receiver and two transmitters (one close to the receiver; the other far away). If both transmitters transmit simultaneously and at equal powers, then due to the inverse square law the receiver will receive more power from the nearer transmitter. This makes the farther transmitter voice more difficult to understand. Since one transmission's signal is the other's noise the signal-to-noise ratio (SNR) for the farther transmitter is much lower. If the nearer transmitter transmits a signal that is orders of magnitude higher than the farther transmitter then the SNR for the farther transmitter may be below detectability and the farther transmitter may just as well not transmit. This effectively jams the communication channel. In CDMA systems this is commonly solved by dynamic output power adjustment of the transmitters. That is the closer transmitters use less power so that the SNR for all transmitters at the receiver is roughly the same. This sometimes can have a noticeable impact on battery life, which can be dramatically different depending on distance from the base station.<br>
+|align = "center"| [http://www.dolcera.com/website_prod/tools Dolcera Tools]
-[[Image:cdma16.jpg]]
+|-
-====Power Control:==== As the propagation losses between BS and MS's are different according to individual communication distances, the received levels at the base station are different from each other when all mobile stations transmit their signals at the same power. Moreover, the received level fluctuates quickly due to fading. In order to maintain the strength of received signal level at BS, power control technique must be employed in CDMA systems.<br>.
+|}
-[[Image:cdma17.jpg]]<br>
+<br>
-Power control can be implemented in two ways : open loop power control and closed loop power control<br>
+===Code Hopping Algorithm===
-[[Image:cdma18.jpg]]
+According to one of the methods of dynamic power control (Code Hopping) used in W-CDMA technology, the Rate Information (RI) field in the uplink control channel in W-CDMA frame can be used to notify the base station about the variable bit rates (VBR) it wants to send, then the base station assigns a new spreading factor for each data rate and hence the optimal power calculation is done according to the spreading factor as follows.<br> Spreading factor(Gi) is defined as the ratio of bandwidth of the system to the data rate of the radio frame.
-'''Effect of Power Control''' Power control is capable of compensating the fading fluctuation. Received power from all MS are controlled to be equal.　Near-Far problem is mitigated by the power control.
-[[Image:cdma19.jpg]]
-==Quality of Service(QoS)==
-CDMA is being accepted as a third generation system and a specific feature of 3G system is that it offers a radio interface adapted for all kinds of services and combination of services(data,voice,image etc). The big issue is of multiplexing of these services which have do not have the same demands in terms of quality of service(QoS) which can be represented as BER(bit error rate),processing delay,frame error rate etc. Different QoS will require different channel encoding and interleaving strategies. The demand of BER can be satisfied when the coding bits have atleast a code dependent ratio Eb/I(ratio of bit energy to interference). There are several influences that might change system performance(BER) and hence Eb/I ratio, of which the most effective is variation of Bit Rate by a step of '''Rate Matching'''. <br><br>
-===Rate Matching and QoS===
-The patent '''EP 1385290 titled Method for balancing Eb/I ratio in a service multiplexing CDMA system and a telecommunication system using this method''' targets at this concept of Rate matching and introduces an algorithm of calculating effective data output bits by a process of repetition or puncturing of the input bits governed by a '''rate matching ratio''' and '''puncturing ratio''' received from the sending entity(can be BS or MS). The following framework highlights the various steps involved in providing variable QoS.
-===Power Control, Rate Matching and QoS===
-According to one of the methods of dynamic power control (Code Hopping) used in W-CDMA technology, the Rate Information (RI) field in the uplink control channel in W-CDMA frame can be used to notify the base station about the variable bit rates (VBR) it wants to send, then the base station computes and assigns optimal powers according to the new spreading factor for each radio frame. Spreading factor(Gi) is defined as the ratio of bandwidth of the system to the data rate of the radio frame.
 Mathematically,<br>
 '''Gi = W / Ri''',where W=system bandwidth which is a constant for a system and Ri= data rate of radio frame.<br>
 A power index (gi) is calculated from this Spreading Factor(Gi) using the following expression<br>
-'''gi=   (gi / (gi+Gi))''', where gi is minimum QoS for the ith session which is a constant.<br>
+'''gi=   (vi / (vi+Gi))''', where vi is minimum QoS for the ith session which is a constant.<br>
-This power index will ascertain the optimal power to be alloted to each service channel.<br>
+This power index will ascertain the optimal power to be alloted to each service channel(each data rate for different services).<br>
 '''Pi = (gi*No*W )/ (Hi*(1-(Sgj)'''<br>
-where No is AWGN(Additive White Guassian Noise)a constant,<br> Hi is path loss which is dependent on the distance and is a costant for a path,<br> and Sgj is sum of the power index of all the sessions which is constant for all sessions of the radio frame. <br>
+where No is AWGN(Additive White Guassian Noise)a constant,<br>
-From the above analysis, we observe that Bit Rate is inversely proportional to Spreading factor which will inversely effect the power index and hence the optimal power. Therefore, the Bit Rate and Optimal power go hand in glove and have the same effect on Eb/I and QoS.
+Hi is path loss which is dependent on the distance and is a constant for a path,<br>
-The method and algorithm to schedule optimal power is detailed in the IEEE paper '''Dynamic Resource Scheduling for Variable QoS Traffic in W-CDMA Ozgur Gurbuz, Henry Owen'''.
+and Sgj is sum of the power index of all the sessions which is constant for all sessions of the radio frame.
-Thus we conclude that by adjusting the optimal power we are actually trying to implement a rate matching step.
-[[Media:ieee1.pdf]]
-===Power control and QoS===
+From the above analysis, we observe that when the mobile is sent the optimal power at which it should transmit. It can backtrack and calculate the power index and spreading factor and hence the Data rate is changed accordingly. This step can be considered to be an equivalent to the Rate Matching Algorithm explained above. The method and algorithm to schedule optimal power is detailed in the IEEE paper 765366 [[Media:IEEEGurbuz.pdf|Dynamic Resource Scheduling for Variable QoS Traffic in W-CDMA - Ozgur Gurbuz, Henry Owen]].
-SPEECH transmission is the main service supported by the first two generations of mobile communication systems. However, future systems should be able to handle a wide variety of different services with bit rate requirement ranging from a few kilobits/s to as much as 2 Mb/s. There are many ways to design a CDMA system to support multirate services . One way to do so is to spread all signals, independent of the bit rate, to the same bandwidth . This is done by keeping the chip rate constant. Users transmitting at low bit rate thus have a high processing gain. This allows those users to transmit at a lower power. Therefore, the conventional constant received power scheme is not appropriate in such a multirate system. A more sophisticated power control scheme is needed to achieve diverse quality of service (QoS) and rate requirement. One such scheme which explores the relationship between the data rate, the QoS, and the transmit power is presented in the IEEE paper '''Power Control and Rate Management for Wireless Multimedia CDMA Systems Chi Wan Sung, Member, IEEE, and Wing Shing Wong, Senior Member, IEEE.'''
-===Dynamic Resource Scheduling and QoS===
+Thus, we conclude that by adjusting the optimal power we are actually trying to implement a rate matching step.
-Dynamic Resource Scheduling (DRS) has been proposed as an adaptive resource management and QoS
-provisioning framework applicable to W-CDMA systems. Various spreading strategies like Fixed Spreading Gain (FSG), Variable Spreading Gain (VSG) and Multi Code (MC) strategies  and their performance is compared in terms of power saving, resource allocation and QoS stability in the IEEE paper '''DYNAMIC RESOURCE SCHEDULING STRATEGIES FOR QOS IN W-CDMA by Ozgur Gurbuz, Henry Owen.''' VSG-DRS and MC-DRS outperform the FSG-DRS for capacity as a result of the statistical multiplexing gain created by adaptive bandwidth usage.
+===Dynamic Resource Scheduling(DRS) Algorithm===
+The Mobile Station(MS) performs Matching of Traffic Descriptors such as Peak Cell Rate(PRC),Sustainable Cell Rate(SCR)  and obtains the connection parameters like average cell rate, SIR, Delay from them. These parameters are sent to the Base Station(BS) where they are queued in a FIFO. The BS determines a spreading factor which allocates the Orthogonal Varible Spread code(OVSF) using '''Gi = W / Ri''',where W=system bandwidth which is a constant for a system and Ri= data rate of radio frame.<br> The base station calculates a value of power index '''gi=   (vi / (vi+Gi))'''and hence Power levels using '''Pi = (gi*No*W )/ (Hi*(1-(Sgj))''', where S stands for sumof, and transmits them to the MS. This information is conveyed to the MS using TPC(Transmission Power Control) bits and a closed loop power control method as explained in section 5.6 above is performed to obtain the final value of power at which transmission should be done.The method and algorithm to schedule optimal power using Dynamic Resource Scheduling is detailed in the IEEE paper 765366 [[Media:IEEEGurbuz.pdf|Dynamic Resource Scheduling for Variable QoS Traffic in W-CDMA - Ozgur Gurbuz, Henry Owen]].
+===Optimal Power Control Algorithm===
+The Base Station receives a Pilot Signal from the Mobile station and calculates BER based on Distance,Transmission rate and No of Users in the Cell. Ptk is the transmitted signal power which is expressed by the power control function g ( rt , k ), a function of the distance from the mobile to
+base station,
+'''Ptk= g(rt,k)Po'''
+where Po is the maximum transmission power. The optimum power functions are transmitted to the Mobile station which calculates the optimal power and starts transmitting at that value. Thus meeting the required QoS parameters.The method and algorithm for optimal power control is detailed in the IEEE paper 503476 [[Media:IEEEYao.pdf|Optimal power control law for Multi-media - Multi-rate CDMA systems
+- Shee Yao and Evaggelos Geraniotis
+]].
+==Research Activity (Non Patent) in the Period (1991-2003)==
+NOTE: The analysis presented below is with respect to the IEEE Papers published between 1991-2003  which focus on the aspect of Quality of Service and its Management using various paramters like Rate matching, Power control, Variable Spreading Factor etc.
+[[Image:Publication_Year.JPG|center|thumb|500 px|Number of publications VS Year of publication]]
+The above analysis suggests a increase in the Research activity in the area of QoS Management in the year 1999.
+[[Image:Publishers.JPG|center|thumb|500 px|Publisher VS number of publications during(1991-2003)]]
+It is to be noted that the non patent research is attributed mostly to universities in USA and Asia Pacific. The mention of '''IEEE member''' in the above graph indicates the absence of information about the parent department of the Researcher.
+[[Image:CDMA_-_3D.JPG|center|thumb|500 px|Graph showing number of publications by the publishers during 1991-2003]]
 ==Conclusion==
-Substantial amount of research has been done in the field of QoS in CDMA communication system in the year 1998-99 and this has led to the invention of multitude of methodologies ranging from power control to Rate matching and so on with the sole aim of improving QoS.
+Substantial amount of research has been done in the field of QoS in CDMA communication system in the year 1998-99 and this has led to the invention of multitude of methodologies ranging from power control to Rate matching and Dynamic Resource scheduling, all with the sole aim of improving QoS.
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Difference between revisions of "Quality of Service on CDMA platforms"

Latest revision as of 23:37, 5 August 2009

Contents

Cellular communication

Quality of Service(QoS)

Need for Rate Matching

QoS Management Algorithms

Rate Matching Algorithm

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Code Hopping Algorithm

Dynamic Resource Scheduling(DRS) Algorithm

Optimal Power Control Algorithm

Research Activity (Non Patent) in the Period (1991-2003)

Conclusion

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