CDMA Basics - Revision history

Raiyani: /* Near Far Problem */

2011-03-10T23:46:25Z

‎Near Far Problem

Raiyani: /* Near Far Problem */

2011-03-10T23:38:52Z

‎Near Far Problem

Manikandan: /* Contact Dolcera */

2009-08-06T06:36:49Z

‎Contact Dolcera

Manikandan: /* Code Division Multiple Access */

2009-08-06T06:36:35Z

‎Code Division Multiple Access

Manikandan: /* Contact Dolcera */

2009-04-30T08:19:43Z

‎Contact Dolcera

Manikandan: /* Power Control */

2009-04-30T07:59:12Z

‎Power Control

121.247.93.141: /* Handoff */

2007-07-29T06:35:33Z

‎Handoff

121.247.93.141: /* Handoff */

2007-07-29T06:30:32Z

‎Handoff

121.247.93.141: /* Cellular System Architecture */

2007-07-29T06:29:30Z

‎Cellular System Architecture

121.247.93.141: /* Frequency Reuse */

2007-07-29T06:29:05Z

‎Frequency Reuse

@@ Line 92: / Line 92: @@
 [[Image:cdma15.jpg|thumb|center|600px|RAKE receiver]]
 === Near Far Problem ===
-The problem is best 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 (Since, '''Pr= Pt/ (4*Pi*d/lambda)^2''', '''Pr''' is received power, '''Pt''' is the transmitted power, '''d''' is the distance between the stations, '''lambda''' is the wavelength of operation and '''Pi''' is 3.14159265....), 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.
+The problem is best 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 (Since, '''Pr= Pt/ (4*Pi*d/lambda)^2''', '''Pr''' is received power, '''Pt''' is the transmitted power, '''d''' is the distance between the stations, '''lambda''' is the wavelength of operation and '''Pi''' is 3.14159265), 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.
 [[Image:cdma16.jpg|thumb|600px|center|Dynamic output power adjustment for CDMA transmitters]]

@@ Line 92: / Line 92: @@
 [[Image:cdma15.jpg|thumb|center|600px|RAKE receiver]]
 === Near Far Problem ===
-The problem is best 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 (Since, '''Pr= Pt/ (4*Pi*d/lambda)^2''', '''Pr''' is received power, '''Pt''' is the transmitted power, '''d''' is the distance between the stations, '''lambda''' is the wavelength of operation and '''Pi''' is 3.1428....), 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.
+The problem is best 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 (Since, '''Pr= Pt/ (4*Pi*d/lambda)^2''', '''Pr''' is received power, '''Pt''' is the transmitted power, '''d''' is the distance between the stations, '''lambda''' is the wavelength of operation and '''Pi''' is 3.14159265....), 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.
 [[Image:cdma16.jpg|thumb|600px|center|Dynamic output power adjustment for CDMA transmitters]]

← Older revision		Revision as of 06:36, 6 August 2009
Line 104:		Line 104:
	[[Image:cdma19.jpg]]		[[Image:cdma19.jpg]]

		+	==<span style="color:#C41E3A">Like this report?</span>==
		+	<p align="center"> '''This is only a sample report with brief analysis''' <br>
		+	'''Dolcera can provide a comprehensive report customized to your needs'''</p>
		+	{\|border="2" cellspacing="0" cellpadding="4" align="center" "
		+	\|style="background:lightgrey" align = "center" colspan = "3"\|'''[mailto:info@dolcera.com <span style="color:#0047AB">Buy the customized report from Dolcera</span>]'''
		+	\|-
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		+	\|align = "center"\| [http://www.dolcera.com/website_prod/services/business-research-services Market Research Services]
		+	\|align = "center"\| [http://www.dolcera.com/website_prod/tools/patent-dashboard Purchase Patent Dashboard]
		+	\|-
		+	\|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]
		+	\|align = "center"\| [http://www.dolcera.com/website_prod/industries Industry Focus]
		+	\|-
		+	\|align = "center"\| [http://www.dolcera.com/website_prod/services/ip-patent-analytics-services/patent-search/patent-landscapes Patent Search Services]
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		+	\|-
		+	\|}
		+	<br>
	==Contact Dolcera==		==Contact Dolcera==

@@ Line 39: / Line 39: @@
 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 for the time switching.
 [[Image:cdma10.jpg|thumb|600px|center|TDMA]]
 === Code Division Multiple Access ===

@@ Line 85: / Line 85: @@
 ==Contact Dolcera==
-'''Samir Raiyani'''
+{| style="border:1px solid #AAA; background:#E9E9E9" align="center"
+|-
-'''201 A South Delaware St. #306'''
+! style="background:lightgrey" | Samir Raiyani
-'''San Mateo, CA 94401 USA'''
+|-
-'''Phone: +1-650-269-7952'''
+| '''Email''': [mailto:info@dolcera.com info@dolcera.com]
-'''Fax: +1-866-690-7517'''
+|-
-'''info@dolcera.com'''
+| '''Phone''': +1-650-269-7952

← Older revision		Revision as of 07:59, 30 April 2009
Line 82:		Line 82:
	'''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.		'''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]]		[[Image:cdma19.jpg]]
		+
		+	==Contact Dolcera==
		+
		+	'''Samir Raiyani'''
		+
		+	'''201 A South Delaware St. #306'''
		+	'''San Mateo, CA 94401 USA'''
		+	'''Phone: +1-650-269-7952'''
		+	'''Fax: +1-866-690-7517'''
		+	'''info@dolcera.com'''

@@ Line 26: / Line 26: @@
 ==== Handoff ====
-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
+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, theprocess 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==

@@ Line 27: / Line 27: @@
 ==== Handoff ====
-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.
+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==

@@ Line 62: / Line 62: @@
 === Frequency Reuse ===
 The number of radio channel frequencies is 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.
 === Soft Handoff ===