RF Technologies and Sectorization EECS

Duplex Duplex: a point-to-point system composed of 2 connected parties/devices that can communication with one another in both directions. Full duplex: both parties can communicate with each other simultaneously. – Examples: telephone Half duplex: each party can communicate with the other but not simultaneously. – Example: walkie-talkie two-way radio Simplex: one device transmits and the others can only "listen” – Example: broadcast radio and TV, surveillance cameras, baby monitors

Full Duplex Emulation Emulates full duplex communication over a half duplex communication link. Time-division duplexing (TDD) Frequency-division duplexing (FDD)

Time-Division Duplexing Applying time division multiplexing to separate uplink and downlink signals. Suitable for cases where there is asymmetry of the uplink and downlink data rates. More time slots are allocated as data rate increases. Examples: – UMTS 3G air interface TD-CDMA for indoor communications – Chinese TD-SCDMA 3G air interface and TD-LTE 4G

Frequency-Division Duplexing The transmitter and receiver operate at different frequencies. Can be efficient in the case of symmetric traffic. – TDD: waste bandwidth during switch-overs; higher latency; more complex circuitry. Examples: – most cellular systems (cdma2000, UMTS/W-CDMA) – IEEE WiMax

Cellular Frequency Bands (4.3) The 850-MHz Band The 1900-MHz Band The 700-MHz Band The 2100-MHz “AWS” Band 6

The 850-MHz Band. The 850-MHz spectrum (in use since 1983) had been unused for years and even TV industry did not use the spectrum. 7

Benefits of 850-MHz Frequency Has a very short signal wavelength (i.e., 12 in). Tends to be line of sight, similar to light itself. Easily reflected off buildings, cars, and trucks. Easily absorbed by foliage (i.e., trees and the forest). – Good: efficient frequency re-use – Bad: signal attenuation 8

The 1900-MHz Band Allocated by the FCC to the “PCS” carriers in PCS Service launched in Also called “PCS band”. Signal strength of 850-MHz spectrum is better than 1900-MHz spectrum in hard-to-reach places. – New 700-MHz spectrum will be even better than the 850-MHz spectrum in this regard 9

Illustrating 1900-MHz Band The 1900-MHz (“PCS”) frequency band. Note the physical separation between the multiple blocks. ADBEFC License-exempt PCS A′D′B′E′F′C′ 15 MHz5 MHz15 MHz5 MHz 15 MHz 5 MHz15 MHz5 MHz 15 MHz

The 700-MHz Band Until 2009, a key section of the 700-MHz spectrum band was owned by broadcasters and used for analog television. – In 2009 it was turned over to the federal government Able to penetrate walls. Desirable for broadband communications in general and public-safety uses in particular. Carriers who purchased 700-MHz licenses intend to use them for 4G/LTE deployments. 11

Categories and Cost Lower 700-MHz: The lower band is 48 MHz. Upper 700-MHz: The upper band is 60 MHz. Cost of building a nationwide wireless network – Over the 700-MHz spectrum is around $2 billion – Over the 1900-MHz PCS band is around $4 billion Costs are lower in rural areas, due to less interference and wide-open spaces. – Because each tower broadcasting at 700 MHz covers twice as many square miles 12

Auction of 700-MHz UHF Spectrum The 2008 auction divided the 700-MHz UHF spectrum into five blocks: – Block A: 12-MHz bandwidth – Block B: 12-MHz bandwidth – Block C: 22-MHz bandwidth – Block D: 10-MHz bandwidth – Block E: 6-MHz bandwidth Total of $ billion raised in the auction. – Verizon Wireless and AT&T Mobility together accounted for $16.3 billion of the total revenue 13

Illustrating 700-MHz Spectrum The 700-MHz frequency band. Most carriers who have purchased this spectrum intend to use it for 4G / LTE deployments. 14

The 2100-MHz AWS Band AWS: Advanced Wireless Service Used for mobile voice and data services, video, and messaging. – Used in the United States and Canada. Frequency range: – From 1710 to 1755 MHz for the uplink – From 2110 to 2155 MHz for the downlink AWS frequency bands were auctioned in the United States in the summer of

Illustrating 2100-MHz “AWS” Band The AWS/2100-MHz spectrum band. 16

In-Building Coverage (4.4) Some large office buildings have a metallic coating, usually green or gold, added to their window glass to reduce the degree to which heat from direct sunlight will warm the buildings. The coating makes it difficult for RF to penetrate these buildings. Solution: use a microcell in the building. 17

Radio Frequency Channelization and Spectrum Allocation (4.6) Today, all channelization occurs using “automatic frequency planning” tools. – These sophisticated software programs automate most, if not all, of the frequency and channel assignments throughout a wireless network. 18

Paired Channels All wireless transmissions require a paired channel to function. Two radio channels are required for every wireless transmission—one for transmit, one for receive. Mobile transmit frequency is the same as base station receive frequency and base station transmit frequencies are the same as mobile receive frequencies. 19

Forward Channel The channel transmitted from the base station to the subscriber’s mobile phone is known as the downlink, or the forward channel. – A paired channel is the combination of the forward channel. When the channels use different frequencies, this is known as frequency-division duplexing. When the channels use the same frequency, it is known as time-division duplexing. 20

Illustrating Paired Channels Paired channels in a wireless system. One channel is required for the uplink, and one channel for the downlink. 21

Channel Spacing When analog AMPS was the only technology used, channel spacing referred to the amount of radio spectrum that was allocated to every cellular transmission. Today, the majority of wireless transmissions use CDMA or W-CDMA technology. Automatic Frequency Planning (AFP) tools: – Today, all frequency and “channel” planning and assignments are done via these software tools 22

Control Channels Data signaling channel that handles the administrative overheads. – Also called “pilot” channel Each cell base station in a wireless system has at least one control channel assigned to it. – In sectorized base stations, each sector will have its own control channel On pressing the send button when placing a call, the phone again rescans for the strongest control channel signal in its assigned frequency band. 23

Administration Tasks of Control Channels Setup of wireless calls, both mobile-originated and mobile-terminated, and locating (paging) mobile phones. Collecting call information. Collecting traffic data from base stations. Autonomous mobile registration. Initiating or assisting in mobile call-handoffs. 24

Example of Control Channels 25

Frequencies in Control Channels Control channel frequencies will be different for each wireless carrier in every market. Like all carrier-assigned frequencies, control channel frequencies are also programmed into the cell phones during the manufacturing process. 26

Sectorization (5.7) It’s necessary to develop a means to increase systems’ capacity without having constantly split cells (costly undertakings). We sectorize the base stations in order to obtain more capacity from each base station deployment.

Migration from Omnidirectional Antenna Replacement of Omnidirectional antenna at base stations is of the ways to increase the capacity of a cellular network: – With three (or six) directional (i.e., sector) antennas of 120 (or 60) degrees beamwidths. – Each sector is viewed as a new cell, with its own (set of) frequencies/channels. – This migration from an omni cell to a sectorized cell occurs at the same physical base station location.

Illustrating Conversion from Omni to Sectorized Cells Conversion from omnidirectional cell site configuration to sectorized cell site configuration.

Benefits of Sectorization Substantially reduces the interference among co- channel cells. Allows for more dense degree of frequency reuse. Range of each sector is bit larger than omni cell. The directional antennas supporting each sector are collocated at the same base station. – All base station/radio equipment for each “subcell,” or sector, is housed in the same base station shelter as well.

Objective of Sectorization To support 360-degree coverage from a single location: – With a three-sectored site, 120-degree beamwidth sector antennas would be used. – With a four-sectored site, 90-degree or narrower beamwidth sector antennas would be used. – With a six-sectored site, 60-degree beamwidth antennas would be used.

Sectorization vs Wireless engineering and Operations Sectorization facilitates wireless engineering and operations in the following ways: – Minimizes or eliminates co-channel interference. – Optimizes the frequency-reuse plan. – Increases the capacity of any given coverage area when compared to the capacity that would be offered using omni antennas. Each sector has its own assignment of frequencies, radio channels and control channel.

Illustrating Sectorization of Cell Sites Sectorization of cell sites using 120-degree beamwidth antennas, resulting in three sectors (alpha, beta and gamma) per cell. Note the coverage overlap between cell sites and sectors.