Editing Evolution-Data Optimized (section)

=== EV-DO Rel. 0 (TIA-856 Release 0) ===
The initial design of EV-DO was developed by [[Qualcomm]] in 1999 to meet [[IMT-2000]] requirements for a greater-than-2&nbsp;Mbit/s down link for stationary communications, as opposed to mobile communication (i.e., moving cellular phone service). Initially, the standard was called High Data Rate (HDR), but was renamed to 1xEV-DO after it was ratified by the [[International Telecommunication Union]] (ITU) under the designation '''TIA-856'''. Originally, 1xEV-DO stood for "1x Evolution-Data Only", referring to its being a direct evolution of the [[CDMA2000|1x]] (1xRTT) air interface standard, with its channels carrying only data traffic. The title of the 1xEV-DO standard document is "cdma2000 High Rate Packet Data Air Interface Specification", as cdma2000 (lowercase) is another name for the 1x standard, numerically designated as TIA-2000.

Later, due to possible negative connotations of the word "only", the "DO"-part of the standard's name 1xEV-DO was changed to stand for "Data Optimized", the full name - EV-DO now stands for "Evolution-Data Optimized." The 1x prefix has been dropped by many of the major carriers, and is marketed simply as EV-DO.<ref name="qualcomm">{{cite web |url=http://www.qualcomm.com/technology/1xev-do.html |archive-url=https://archive.today/20061104082805/http://www.qualcomm.com/technology/1xev-do.html |url-status=dead |archive-date=2006-11-04 |title=CDMA2000 1xEV-DO |publisher=QUALCOMM Technology and Solutions }}</ref> This provides a more market-friendly emphasis of the technology being data-optimized.

==== Forward link channel structure ====
The primary characteristic that differentiates an EV-DO channel from a 1xRTT channel is that it is [[Time-division multiplexing|time multiplexed]] on the forward link (from the tower to the mobile). This means that a single mobile has full use of the forward traffic channel within a particular geographic area (a sector) during a given slot of time. Using this technique, EV-DO is able to [[Digital modulation method|modulate]] each user’s time slot independently. This allows the service of users in favorable RF conditions with very complex [[modulation]] techniques while also serving users in poor RF conditions with simpler (and more redundant) signals.<ref name="Performance">{{Cite journal |first1=Qi |last1=Bi |author2=S. Vitebsky |title=Performance analysis of 3G-1X EV-DO high data rate system |journal=IEEE Wireless Communications and Networking Conference |publisher=IEEE |pages=389–395 |date=17–21 March 2002}}</ref>

The forward channel is divided into slots, each being 1.667 ms long. In addition to user traffic, overhead channels are interlaced into the stream, which include the 'pilot', which helps the mobile find and identify the channel, the [[MAC address|Media Access Channel (MAC)]] which tells the mobile devices when their data is scheduled, and the 'control channel', which contains other information the network needs the mobile devices to know.

The [[modulation]] to be used to communicate with a given mobile unit is determined by the mobile device itself; it listens to the traffic on the channel, and depending on the receive signal strength along with the perceived multi-path and fading conditions, makes a best guess as to what data-rate it can sustain while maintaining a reasonable frame error rate of 1-2%. It then communicates this information back to the serving sector in the form of an integer between 1 and 12 on the "Digital Rate Control" (DRC) channel. Alternatively, the mobile can select a "null" rate (DRC 0), indicating that the mobile either cannot decode data at any rate, or that it is attempting to [[handoff|hand off]] to another serving sector.<ref name="Performance" />

The DRC values are as follows:<ref name="Lucent">{{cite web |url=http://www.cdg.org/resources/white_papers/files/Lucent%201xEV-DO%20Rev%20O%20Mar%2004.pdf |title=A Forward Link Performance Study of the 1xEV-DO Rel. 0 System Using Field Measurements and Simulations |access-date=2008-01-18 |last=Bi |first=Qi |date=March 2004 |publisher=[[Alcatel-Lucent|Lucent Technologies]] |archive-date=2008-02-16 |archive-url=https://web.archive.org/web/20080216101314/http://www.cdg.org/resources/white_papers/files/Lucent%201xEV-DO%20Rev%20O%20Mar%2004.pdf |url-status=dead }}</ref>

{| class="wikitable"
|-
! DRC Index
! [[Bit rate|Data rate (kbit/s)]]
! Slots scheduled
! Payload size (bits)
! [[Code rate|Code Rate]]
! [[Modulation]]
! [[Signal-to-noise ratio|SNR]] Reqd.
|-
| 1
| 38.4
| 16
| 1024
| 1/5
| [[QPSK#Quadrature phase-shift keying (QPSK)|QPSK]]
| -12
|-
| 2
| 76.8
| 8
| 1024
| 1/5
| [[QPSK#Quadrature phase-shift keying (QPSK)|QPSK]]
| -9.6
|-
| 3
| 153.6
| 4
| 1024
| 1/5
| [[QPSK#Quadrature phase-shift keying (QPSK)|QPSK]]
| -6.8
|-
| 4
| 307.2
| 2
| 1024
| 1/5
| [[QPSK#Quadrature phase-shift keying (QPSK)|QPSK]]
| -3.9
|-
| 5
| 307.2
| 4
| 2048
| 1/5
| [[QPSK#Quadrature phase-shift keying (QPSK)|QPSK]]
| -3.8
|-
| 6
| 614.4
| 1
| 1024
| 1/3
| [[QPSK#Quadrature phase-shift keying (QPSK)|QPSK]]
| -0.6
|-
| 7
| 614.4
| 2
| 2048
| 1/3
| [[QPSK#Quadrature phase-shift keying (QPSK)|QPSK]]
| -0.8
|-
| 8
| 921.6
| 2
| 3072
| 1/3
| [[8PSK|8-PSK]]
| 1.8
|-
| 9
| 1228.8
| 1
| 2048
| 2/3
| [[QPSK#Quadrature phase-shift keying (QPSK)|QPSK]]
| 3.7
|-
| 10
| 1228.8
| 2
| 4096
| 1/3
| [[QAM#Rectangular QAM|16-QAM]]
| 3.8
|-
| 11
| 1843.2
| 1
| 3072
| 2/3
| [[8PSK|8-PSK]]
| 7.5
|-
| 12
| 2457.6
| 1
| 4096
| 2/3
| [[QAM#Rectangular QAM|16-QAM]]
| 9.7
|}

Another important aspect of the EV-DO forward link channel is the scheduler. The scheduler most commonly used is called "[[proportional fair]]". It's designed to maximize sector throughput while also guaranteeing each user a certain minimum level of service. The idea is to schedule mobiles reporting higher DRC indices more often, with the hope that those reporting worse conditions will improve in time.

The system also incorporates [[Hybrid automatic repeat-request|Incremental Redundancy Hybrid ARQ]]. Each sub-packet of a multi-slot transmission is a [[Turbo code|turbo-coded]] replica of the original data bits. This allows mobiles to acknowledge a packet before all of its sub-sections have been transmitted. For example, if a mobile transmits a DRC index of 3 and is scheduled to receive data, it will expect to get data during four time slots. If after decoding the first slot the mobile is able to determine the entire data packet, it can send an early acknowledgement back at that time; the remaining three sub-packets will be cancelled. If however the packet is not acknowledged, the network will proceed with the transmission of the remaining parts until all have been transmitted or the packet is acknowledged.<ref name="Performance" />

==== Reverse link structure ====
The reverse link (from the mobile back to the [[Base Transceiver Station]]) on EV-DO Rel. 0 operates very similar to that of [[CDMA2000|CDMA2000 1xRTT]]. The channel includes a reverse link pilot (helps with decoding the signal) along with the user data channels. Some additional channels that do not exist in 1x include the DRC channel (described above) and the ACK channel (used for [[Hybrid automatic repeat-request|HARQ]]). Only the reverse link has any sort of [[power control]], because the forward link is always transmitted at full power for use by all the mobiles.<ref name="Lucent" /> The reverse link has both open loop and closed loop power control. In the open loop, the reverse link transmission power is set based upon the received power on the forward link. In the closed loop, the reverse link power is adjusted up or down 800 times a second, as indicated by the serving sector (similar to [[CDMA2000|1x]]).<ref>[http://www.cdg.org/technology/3g/advantages_cdma2000.asp CDG: Advantages of CDMA2000] {{webarchive |url=https://web.archive.org/web/20081023022338/http://www.cdg.org/technology/3g/advantages_cdma2000.asp |date=October 23, 2008 }}</ref>

All of the reverse link channels are combined using [[code-division multiple access|code division]] and transmitted back to the base station using [[BPSK]]<ref>{{cite web|url=http://rfmw.em.keysight.com/rfcomms/refdocs/1xevdo/1xevdo_gen_rtap_rate.html|title=RTAP Rate|work=keysight.com|access-date=14 August 2015}}</ref> where they are decoded. The maximum speed available for user data is 153.2&nbsp;kbit/s, but in real-life conditions this is rarely achieved. Typical speeds achieved are between 20-50&nbsp;kbit/s.