Chapter 10: Cellular Wireless Network
10 to 50 frequencies
frequencies assigned to each cell depending on traffic expected
WiMAX
from the IEEE 802.16 committee, which has developed standards for high-speed fixed wireless operations uses a pure OFDMA approach of both uplink (UL) and downlink (DL) retains a role as the technology for fixed broadband wireless access,
mobile radio telephone service
was only provided by a high-power transmitter/receiver
LTE-Advanced and SC-OFDM (single-carrier OFDM).
For the downlink, ______ uses OFDMA and for the uplink _________
diffraction and scattering are the primary means of signal reception.
If there is no clear LOS, such as in an urban area at street level
Frequency borrowing
In the simplest case, frequencies are taken from adjacent cells by congested cells. The frequencies can also be assigned to cells dynamically.
China Mobile
adopted a version of LTE based on time-division duplex (TDD).
ITU
According to ____ IMT-Advanced (or 4G) cellular system must fulfill a number of minimum requirements
Call blocking
After repeated attempts, if all traffic channels are busy, a busy tone is returned
900 MHz and 0.33 m
At a frequency of ____ , which is typical for mobile cellular applications, a wavelength is _____
slow fading
Change in the average received power level due to user passing different height buildings, vacant lots, intersections, etc
base transceiver
In a cellular system, each cell has ________.
adding new channels frequency borrowing cell splitting
In time, as more customers use the system, traffic may build up so that there are not enough frequencies assigned to a cell to handle its calls. A number of approaches have been used to cope with this situation
First Generation (1G)
Original cellular telephone networks provided analog traffic channels Designed to be an extension of the public switched telephone networks Also common in South America, Australia, and China
Signal strength
Strength of signal between BS and mobile unit needs to be strong enough to maintain signal quality Not too strong so as to create co-channel interference the __________ varies dynamically as the mobile unit moves.
Chip rate
depends on desired data rate, the need for error control, and bandwidth limitations
Both LTE TDD and LTE FDD
deployed as each form of the LTE standard has its own advantages and disadvantages
use lower-power systems with shorter radius and to use numerous transmitters/receivers
how to increase the capacity of the system?
Diffraction
occurs at the edge of an impenetrable body that is large compared to the wavelength of the radio wave
4G
provide ultra-broadband Internet access for a variety of mobile devices including laptops, smartphones, and tablet PCs. support Mobile Web access and high-bandwidth applications such as high-definition mobile TV, mobile video conferencing, and gaming services. maximize bandwidth and throughput while also maximizing spectral efficiency.
(824-849 MHz).
transmission from the mobile to the base station
Cellular Network Organization
use of multiple low-power transmitters(100 W or less) Key for mobile technologies area divided into cells
Paging
The MTSO sends a ______message to certain BSs depending on the called mobile number Each BS transmits the ______ signal on its own assigned setup channel
Call accepted
The called mobile unit recognizes its number on the setup channel being monitored and responds to that BS, which sends the response to the MTSO
frequency modulation (FM).
The conversation channels carry the conversations in analog using _______
adding new channels
Typically, when a system is set up in a region, not all of the channels are used, and growth and expansion can be managed in an orderly fashion by ____________..
Call drop
When BS cannot maintain required signal strength the traffic channel to the user is dropped and the MTSO is informed
Call termination
When one of the two users hangs up, the MTSO is informed and the traffic channels at the two BSs are released.
intersymbol interference (ISI).
A second phenomenon, of particular importance for digital transmission
Microcells
As cells become smaller, antennas move from the tops of tall buildings or hills, to the tops of small buildings or the sides of large buildings, and finally to lamp posts, where they form _______. Each decrease in cell size is accompanied by a reduction in the radiated power levels from the base stations and the mobile units are useful in city streets in congested areas, along highways, and inside large public buildings
Encryption:
Because all of the user traffic, as well as control traffic, is digitized in second-generation systems, it is a relatively simple matter to encrypt all of the traffic to prevent eavesdropping
20 or 30 dB
Changes of amplitude can be as much as ______ over a short distance.
base station
Each cell is allocated a band of frequencies and is served by __________. consisting of transmitter, receiver, and control unit approximate center of each cell Each of it is connected to a mobile telecommunications switching office (MTSO), with one MTSO serving multiple BSs
Fading
Even if signal strength is within an effective range, signal propagation effects may disrupt the signal and cause errors Caused by changes in transmission path(s) Time variation of received signal
Calls to/from fixed and remote mobile subscriber
MTSO connects to the PSTN (public switched telephone network)
signal strength and signal propagation effects.
Mobile radio communication introduces complexities not found in wire communication or in fixed wireless communication. two general areas of concern are _______ and _________
frequency reuse patterns: reuse factor
N = number of cells in a repetitious pattern (each cell in the pattern uses a unique band of frequencies)
Error detection and correction:
The digital traffic stream of second-generation systems also lends itself to the use of error detection and correction techniques,
forward error correction, adaptive equalization, and diversity techniques
The efforts to compensate for the errors and distortions introduced by multipath fading fall into categories. techniques from this categories are combined to combat the error rates encountered.
the evolved packet core (EPC)
The operator, or carrier, network that interconnects all of the base stations of the carrier
Control channels and traffic channels
Two types of channels are available between the mobile unit and the base station
Cell sectoring
a cell is divided into a number of wedge-shaped sectors, each with its own set of channels, typically three or six sectors per cell. Each sector is assigned a separate subset of the cell's channels, and directional antennas at the base station are used to focus on each sector.
Diversity
based on the fact that individual channels experience independent fading events refers to frequency diversity or time diversity techniques This technique does not eliminate errors but it does reduce the error rate, since we have spread the transmission out to avoid being subjected to the highest error rate that might occur.
Adaptive equalization
can be applied to transmissions that carry analog information (e.g., analog voice or video) or digital information (e.g., digital data, digitized voice or video) and is used to combat intersymbol interference
Traffic channels
carry a voice or data connection between users.
1.5 km
cell size that is close to practical minimum size
cable based (copper or fiber wires. )
connections between base stations and switching offices in 3G networks
MTSO( mobile telecommunications switching office )
connects calls between mobile units connected to the public telephone or telecommunications network and can make a connection between a fixed subscriber to the public network and a mobile subscriber to the cellular network assigns the voice channel to each call, performs handoffs, and monitors the call for billing information
Mobility management entity (MME):
deals with control signaling related to mobility and security. responsible for the tracking and the paging of UE in idle-mode.
Second-generation 2G
develop to provide higher quality signals, higher data rates for support of digital services, and greater capacity.
Long Term Evolution (LTE)
developed by the Third Generation Partnership Project (3GPP), a consortium of Asian, European, and North American telecommunications standards organization uses pure OFDMA on the downlink but a technique that is based on OFDMA offers enhanced power efficiency for the uplink. become the universal standard for 4G wireless.
CDMA
dominant technology for 3G systems
scattering
it occurs if the size of an obstacle is on the order of the wavelength of the signal or less An incoming signal is scattered into several weaker outgoing signals. its effect is difficult to predict
Home subscriber server (HSS):
maintains a database that contains user-related and subscriber-related information provides support functions in mobility management, call and session setup, user authentication, and access authorization.
Frequency Reuse
objective is to share nearby cell freq w/o interfering each other (allowing the frequency to be used for multiple simultaneous conversations)
Packet data network gateway (PGW):
point of interconnect between the EPC and the external IP networks such as the Internet. IP address/IP prefix allocation and policy control and charging. routes packets to and from the external networks
CDMA Multi rate
provision of multiple fixed-data-rate logical channels to a given user, in which different data rates are provided on different logical channels. advantage: system can flexibly support multiple simultaneous applications from a given user efficiently use available capacity by only providing the capacity required for each service
fast fading
rapid variations in signal strength occur over distances of about one-half a wavelength affects not only mobile phones in automobiles, but even a mobile phone user walking down an urban street.
Digital traffic channels:
supported only by the use of a modem that converts the digital data into analog form.
Circuit switching
supported to enable voice connections between mobile users and phones connected to the PSTN
Cellular radio
technique that was developed to increase the capacity available for mobile radio telephone service typical system would support about 25 channels with an effective radius of about 80 km
Advanced Mobile Phone Service (AMPS)
the most common first-generation system in North America has been the _____ developed by AT&T
(869-894 MHz)
transmission from the base station to the mobile unit
Flat fading or nonselective fading
type of fading in which all frequency components of the received signal fluctuate in the same proportions simultaneously implies that the signal bandwidth of interest is narrower than, and completely covered by, the spectrum affected by the fading.
Control channels
used to exchange information having to do with setting up and maintaining calls and with establishing a relationship between a mobile unit and the nearest BS
controller
used to handle the call process between the mobile unit and the rest of the network
handshake
used to identify the user and register its location takes place between the mobile unit and the MTSO controlling this cell, through the BS in this cell
eNodeB air
whereas the _____ interface is based on OFDMA. embeds its own control functionality, rather than using an RNC (Radio Network Controller) as does a NodeB.
Cellular technology
-the foundation of mobile wireless communications and supports users in locations that are not easily served by wired networks -underlying technology for mobile telephones, personal communications systems, wireless Internet and wireless Web applications, and much more.
Mobile-originated call
A mobile unit originates a call by sending the number of the called unit on the preselected setup channel
Bandwidth
An important design goal for all 3G systems is to limit channel usage to 5 MHz.
diffraction and scattering are generally minor effect
If a mobile unit has a clear LOS to the transmitter reflection may have a significant impact
Cell splitting
In practice, the distribution of traffic and topographic features is not uniform, and this presents opportunities for capacity increase. Cells in areas of high usage can be split into smaller cells
Cell sectoring Microcells
Increasing Capacity
femtocell gateway.
The femtocell connects to the Internet, typically over a DSL, fiber, or cable landline. Packetized traffic to and from the femtocell connects to the cellular operator's core packet network via ______
equalization
The process of it involves some method of gathering the dispersed symbol energy back together into its original time interval. techniques include the use of so-called lumped analog circuits as well as sophisticated digital signal processing algorithms.
handoff
To use a smaller cell, the power level used must be reduced to keep the signal within the cell. Also, as the mobile units move, they pass from cell to cell, which requires transferring of the call from one base transceiver to another. ---The system makes this change without either interrupting the call or alerting the user.
Mobile unit initialization
When the mobile unit is turned on, it scans and selects the strongest setup control channel used for this system
Ongoing call
While the connection is maintained, the two mobile units exchange voice or data signals, going through their respective BSs and the MTSO
all major carriers in the United States, including AT&T and Verizon
adopted a version of LTE based on frequency-division duplex (FDD),
Selective fading
affects unequally the different spectral components of a radio signal significant only relative to the bandwidth of the overall communications channel If attenuation occurs over a portion of the bandwidth of the signal
power of base transceiver controlled
allow comms w/in cell on a given freq limit escaping power to adjacent cells
Forward error correction
applicable in digital transmission applications: those in which the transmitted signal carries digital data or digitized voice or video data the ratio of total bits sent to data bits sent is between 2 and 3 (in mobile wireless application)
Serving gateway (SGW
deals with user data transmitted and received by UEs in packet form, using IP point of interconnect between the radio side and the EPC serves the UE by routing the incoming and outgoing IP packets. It is the anchor point for the intra-LTE mobility (i.e., in case of handover between eNodeBs). packets can be routed from an eNodeB to an eNodeB in another area via the SGW
Channel access:
each channel is dynamically shared by a number of users using time division multiple access (TDMA) or code division multiple access (CDMA).
Femtocells
essential component of the 4G strategy for satisfying demand low-power, short range, self-contained base station. Initially used to describe consumer units intended for residential homes the term has expanded to encompass higher capacity units for enterprise, rural and metropolitan areas. Key attributes include IP backhaul, self-optimization, low power consumption, and ease of deployment. connects to the Internet, typically over a DSL, fiber, or cable landline
NodeB station
interface with subscriber stations (referred to as user equipment (UE)) is based on CDMA,
Hata's model
is an empirical formulation that takes into account a variety of environments and conditions
Okumura [OKUM68] and Hata [HATA80].
model develop that was based on empirical data and to apply that model to a given environment to develop guidelines for cell size The original was a detailed analysis of the Tokyo area and produced path loss information for an urban environment.
Reflection
occurs when an electromagnetic signal encounters a surface that is large relative to the wavelength of the signal. Further, because the mobile antenna is lower than most human-made structures in the area, multipath interference occurs. These reflected waves may interfere constructively or destructively at the receiver
6.5 to 13 km in size
original cells are about ______
third generation (3G)
provide fairly high-speed wireless communications to support multimedia, data, and video in addition to voice Voice quality comparable to the public switched telephone network 144 kbps data rate available to users in high-speed motor vehicles over large areas Symmetrical and asymmetrical data transmission rates Support for both packet-switched and circuit-switched data services
voice over IP (VoIP).
the core cellular network was circuit switched, but for 4G the core is entirely packet switched that is based on IP and supports voice connections
propagation effects
the desired maximum transmit power level at the base station and the mobile units, the typical height of the mobile unit antenna, and the available height of the BS antenna [These factors will determine the size of the individual cell]
frequency diversity
the signal is spread out over a larger frequency bandwidth or carried on multiple frequency carriers most important example of this approach is spread spectrum
space diversity
this involves the physical transmission path For example, multiple nearby antennas may be used to receive the message, with the signals combined in some fashion to reconstruct the most likely transmitted signal
small cell
umbrella term for low-powered radio access nodes that operate in licensed and unlicensed spectrum that have a range of 10 m to several hundred meters.
multiple copies of a signal may arrive at different phases
unwanted effect of multipath propagation if these phases add destructively, signal level relative to noise declines, making signal detection at the receiver more difficult
minimum requirements for IMT cellular system
• Be based on an all-IP packet switched network. • Support peak data rates of up to approximately 100 Mbps for high-mobility mobile access and up to approximately 1 Gbps for low-mobility access such as local wireless access. • Dynamically share and use the network resources to support more simultaneous users per cell. • Support smooth handovers across heterogeneous networks. • Support high quality of service for next-generation multimedia applications.
