Jochen H. Schiller. Mobile. Communications. Second Edition .. German as PDF and PowerPoint™ files, a list of all acronyms, and many links to related sites. Download Mobile Communications By Jochen Schiller – The mobile communications market remains the fastest growing segment of the global computing and. Prof. Dr.-Ing. Jochen H. Schiller raudone.info MC - connections to GSM mobile communications networks have now passed the 3 Billion mark.
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Dr.-Ing. Jochen H. Schiller raudone.info MC - The demand for mobile communication created already decades ago the need for integration of. You can find book mobile communication by jochen schiller in our library and other format like: mobile communication by jochen schiller pdf file mobile. Jochen Schiller, Institute of Informatics, Freuie Universitat Berlin . Mobile Communications (Computer Science) · Telecommunications (Computer Science) .
Front Cover. Pearson Education, - Mobile communication systems - pages Jochen H. Schiller Snippet view - This is a technical introduction to the current developments within Mobile communications.
It allows the reader to assess new developments, how to harness. The mobile communications market remains the fastest growing segment of the In this book Jochen Schiller draws on his extensive experience to provide a. Mobile Communications ebook free download Jochen Schiller. Posted on Tuesday, 16 October by Ketan Dani.
Mobile Communications ebook free. Location dependent services 6. Mobile and wireless devices 7. The most prominent system is the traditional radio: all music and voice use frequencies between, e. However, many different radio stations want to transmit at the same time.
Therefore, all the original signals which use the same frequency range must be modulated onto different carrier frequencies. Other motivations for digital modulation are antenna and medium characteristics. Important characteristics for digital modulation are spectral efficiency, power efficiency and robustness. The receiver then chooses the closest neighbour and assumes that the sender originally transmitted data represented by the chosen point.
The more points a PSK scheme uses the higher are chances that interference noise shifts a transmitted point onto another.
If the gaps between the points are too small, in particular smaller than noise added during transmission, chances are very high that the receiver will map received data onto the wrong point in the constellation diagram please note: data is coded using PSK, the points in the constellation diagram represent codes, these codes are then transmitted it is just simpler to think in points.
Spreading can be achieved by XORing a bit with a chipping sequence or frequency hopping. Guard spaces are now the orthogonality of the chipping sequences or hopping patterns. The higher the orthogonality well, that is not very mathematical, but intuitive , the lower the correlation of spread signals or the lower the collision probability of frequency hopping systems. DSSS system typically use rake receivers that recombine signals travelling along different paths. Recombination results in a stronger signal compared to the strongest signal only.
Cellular systems reuse spectrum according to certain patterns.
Each cell can support a maximum number of users. Using more cells thus results in a higher number of users per km. Additionally, using cells may support user localisation and location based services. Smaller cells also allow for less transmission power thus less radiation!
Well, the downside is the tremendous amount of money needed to set-up an infrastructure with many cells.
Typically, each cell holds a certain number of frequency bands. Neighbouring cells are not allowed to use the same frequencies.
According to certain patterns 7 cluster etc. If the system dynamically allocates frequencies depending on the current load, it can react upon sudden increase in traffic by borrowing capacity from other cells. However, the borrowed frequency must then be blocked in neighbouring cells.
The system assigns a certain time-slot at a certain frequency to a user. If all time-slots at all frequencies are occupied no more users can be accepted. Compared to this hard capacity a CDM system has a so-called soft-capacity compare filling a box with bricks or tissues.
For CDM systems the signal-to-noise-ratio typically limits the number of simultaneous users. The system can always accept an additional user. However, the noise level may then increase above a certain threshold where transmission is impossible.
In CDM systems each additional user decreases transmission quality of all other users the space for the tissues in the box gets tighter. Medium Access Control 3. Thus, if one station transmits a signal all other stations connected to the wire receive the signal. Todays wired networks are star shaped in the local area and many direct connections forming a mesh in wide area networks. In wireless networks, it is quite often the case that stations are able to communicate with a central station but not with each other.
This lead in the early seventies to the Aloha access scheme University of Hawaii. So what is CS Carrier Sense good for in wireless networks? The problem is that collisions of data packets cause problems at the receiver but carrier sensing takes place at the sender.
In wired networks this doesnt really matter as signal strength is almost the same ok, within certain limits all along the wire. In wireless networks CS and CD at the sender doesnt make sense, senders will quite often not hear other stations signals or the collisions at the receiver.
There are no stations exposed as stations do not perform carrier sensing. Hidden stations may cause collisions. The same is true for slotted Aloha the only difference being the slotted character of medium access.
Reservation schemes typically work with a central reservation station which can be heard by all others. Without this condition or equivalent means of distributing reservations the whole scheme will not work.
Thus, there are no hidden or exposed terminals. However, MACA may fail in case of asymmetric communication conditions or highly dynamic topologies stations may move fast into collision range. In TDMA systems terminals measure the signal strength and the distance between sender and receiver. The terminals then adapt transmission power and send signals in advance depending on the distance to the receiver. Terminals in CDMA systems have to adapt their transmission power very often e.
Without this one signal could drown others as the signals are not separated in time. The provider plans the network, i. If the system is running, base stations support the infrastructure in the decision of assigning a certain base station to a terminal.
This is often based on received signal strength or the current capacity. The mobile terminal supports the infrastructure by transmitting information about the received signal strengths. The terminal can furthermore initiate the change of the access point. This is typically an analogue process and requires analogue components. Classical receivers also need filters for receiving signals at certain frequencies. Depending on the carrier frequency different antennas may be needed.
Pure TDMA systems stay on one frequency, all receivers can wait on the same frequency for data. In FDMA systems receivers have to scan different carrier frequencies before they can receive signals. MAC is performed on many different layers. ITU controls worldwide frequency usage. National authorities regulate frequencies in different nations. On the next lower layers network operators perform MAC: frequencies usage is controlled by network planning and current load.
Finally, base stations in mobile phone systems assign frequencies to terminals depending on the current availability. In WLANs network administration assigns frequencies thus forming cells. Typical wired networks simply use different wires however, more elaborated schemes such as echo cancellation are feasible, too. The only requirement is to stay synchronised to be able to receive the right data. This is the standard system in classical telecommunication networks e.
Ethernets, the Internet, wireless LANs etc. Here the advantage is the low overhead when starting communication: terminals dont have to setup connections reserving time slots prior to communication. However, users transmit more and more data compared to voice. Most networks of today are data dominated if the amount of data is considered, not the revenue. Thus, data transmission should be optimised.
While WLANs are optimised for data from the beginning and isochronous audio transmission causes some problems , wide area mobile phone systems started as almost voice only systems. The standard scheme is circuit switched, not packet switched.
Terminals or base stations have to keep a minimum distance. TDMA: Interference happens if senders transmit data at the same time. Countermeasures are tight synchronisation and guard spaces time gap between transmissions.
FDMA: Interference happens if senders transmit data at the same frequency. Thus, different frequencies have to be assigned to senders by organisations, algorithms in base stations, common frequency hopping schemes etc. Furthermore, guard bands between used frequency bands try to avoid interference.
CDMA: Interference happens if senders transmit data using non-orthogonal codes, i. Thus, senders should use orthogonal or quasi-orthogonal codes. As soon as matter is in the way waves travel even slower. Thus, it can happen that a sender senses the medium idle, starts the transmission and just in a moment before the waves reach another sender this second sender senses the medium idle and starts another transmission.
Reservation schemes can also guarantee bandwidth, delay, and maximum jitter. Thus, during the transmission nothing can happen.
Compared to classical Aloha the collision probability is lower because the contention period is kept short compared to the contention-free period where transmission takes place. A disadvantage of reservation schemes is the latency for data transmission.
Before terminals can start transmission they have to reserve the medium. This wastes time in case of a very lightly loaded medium.
What if station C in figure 3. Also implicit reservations can give guarantees after the reservation succeeded. Furthermore, all centralistic systems, i. The lower the correlation is, the better is the user separation.
The receiver can decide more easily for the binary 0 in case of B compared to the binary 1 in case of A. Noise can obviously affect the signal. But still the receiver can distinguish between the two signals our simple example uses perfectly synchronised signals the spread symbols are in phase.
Simply multiply the noise and Bs signal by, let us say, Both results are negative, the receiver can not reconstruct the original data of A, but that of B. This example should just give a rough feeling what the problems are. For our simple problem here we dont see all the effects: the spreading codes are much too short, everything is synchronised.
Telecommunication systems 4.
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Common features are traditional voice support circuit switched , integration into classical fixed telecommunication network, ISDN core network.
Data transmission happens quite often spontaneous with varying data rates.
Thus either too much bandwidth is reserved to accommodate the maximum expected data rate or data transmission experiences long delays due to connection setup. One possible step towards the support of data transmission is the introduction of packet switched services as known from the Internet. Instead of time-based billing providers can now bill based on volume however, application based billing would make even more sense as customers are not interested in bytes but useful applications.
Separation of services supports phased introduction of services and separation of concerns: network providers, service providers, device manufacturers etc. Furthermore, bandwidth is needed for signalling, guard spaces. Specifying all or at least many internal interfaces allows for a larger variety of vendors.
As long as vendors stay with the standardised interfaces equipment of different vendors can be combined and network operators are not completely dependent from one manufacturer. However, reality often looks different and network operators often use only equipment from one or two vendor s. This separation helps changing phones while keeping personal data: users simply insert their SIM in a new mobile phone and can use, e.
However, this is rather a marketing than technical reason. Besides the SIM also the mobile phone itself can store user-related data. Additional user-related data is stored in the VLR responsible for the location area a user is currently in and the HLR of the network operator the user has a contract with.
User data is protected in several ways: authentication centres are protected parts of the HLR residing at the network operator. Inside the core network only temporary identifiers are used, data is encrypted over the air interface weak, but still encrypted , and the content of the SIM is protected via a PIN some cards destroy themselves after being attacked too many times.
Localisation could be terminal assisted: the terminal could gather the current signal strength from all surrounding base stations. Furthermore, using the time of arrival helps calculating the distance. Reflection and attenuation makes the calculation more difficult. If many users move between location areas updates have to take place, i. These updates happen independently on the users activity data transmission, calls etc. For standard scenarios most users stay most of the time within their location area the 2-level hierarchy works well.
However, if, e. More levels of hierarchy could improve scalability but also raises complexity. It simply combines several connections. Basically, the core network needs routers handling the packet stream. Furthermore, the system has to set up a context for each active user, account transmitted data, assign IP addresses etc. This limitation is not because of too strong attenuation, but because of the delay the signals experience. All signals must arrive synchronised at the base station, timing advance adjust the sending point the further away a terminal is the earlier it has to send its data.
With some tricks the diameter can be doubled. The number of channels is operator and regulation dependent. New modulation schemes can offer higher capacity, EDGE is an example.
Furthermore, systems like GPRS offer different levels of error protection this may increase user data rates under good propagation conditions, but does not increase the system capacity.
FDM: Regulation authorities assign channels to operators, operators assign channels to base stations, and base stations assign a certain channel to a terminal during data transmission. TDM: Base stations assign a time-slot or several time-slots to a terminal for transmission. Terminals listen into the medium, receive signals over broadcast channels and synchronise to the frame structure.
Within each time-slot during transmission a midample further improves synchronisation. The terminal itself is responsible for precise synchronisation within the cell. This is very important in TDM systems as otherwise neighbouring data may be destroyed. Experiments show that packets in GPRS may experience heavy delays due to channel access delays: ms for byte packets, several seconds for kbyte packets. Terminals have to access the base station suing a slotted Aloha scheme for the layer 2 signalling connection.
During this connection attempt several terminals may collide and have to repeat the connection attempt.
Mobile Communication By Jochen Schiller Pdf Free Download
During data transmission or voice call no collision can occur. HSCSD has the additional problem of requesting several channels. These may be occupied.
However, this does not cause a collision but a simple denial of the connection request for several channels. Channel assignment and release is handled dynamically in GSM systems. For GPRS, too, data transmission can not cause a collision as the terminal wanting to transmit has to request time-slots firs. After the assignment of time-slots the terminal may access these slots without further collisions.
Depending on the current load, not too many slots may be available; however, network operators try to offer at least one slot per cell for GPRS traffic to offer a minimum data rate. If a TCH exists and more signalling is required e. Each time a user changes the location area this change is reflected in the VLR. Additionally, periodic updates are possible. Roaming includes changing the network operator. This can happen within the same country national roaming or when going to another country international roaming.
The latter is the most common scenario as national roaming typically involves direct competitors. Prerequisite are roaming agreements between the different operators. Precise localisation of users is performed during call setup only paging within the location area. That is all users should see.
These phone numbers are completely independent of the current location of the user. The system itself needs some additional information; however, it must not reveal the identity of users.
During operation within a location area, only a temporary identifier, the TMSI is needed. This hides the identity of a user. These are already some examples for identifiers; however, GSM provides some more: IMEI: MS identification like a serial number ; consists of type approval code centrally assigned , final assembly code, serial number, and spare all three manufacturer assigned.
Consists of the mobile country code 3 digits, e. The mobile network code together with the mobile subscriber identification number forms the national mobile subscriber identity. It consists of a country code 3 digits , a mobile network code 2 digits , and a location area code 16 bit. CI: Within a LA each cell has a unique cell identifier 16 bit.
BSIC: The base transceiver station identity code identifies base stations 6 bit and consists of a 3 bit network colour code and a 3 bit base transceiver station colour code. Another reason could be the current load situation: the network could decide to offload some users from a crowded cell. For the typical steps and types of handover see figures 4. Otherwise the available bandwidth will decrease.
Sure the probability of having several channels available is much lower than having a single channel. For GPRS data rates fluctuate anyway depending on the current load. The same happens during and after handover. There is not even a QoS guarantee for a voice call if the next cell is already completely booked the connection will break upon entering this cell. This is done using a simple PIN. This second authentication is much stronger compared to the PIN. This is because the operator is not really interested in who is using the system as long as it is a valid and paying customer.
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Authentication with the system uses a challenge response scheme with a shared secret on the SIM and in the AuC. GSM does not provide strong encryption end-to-end or MS to the gateway into the fixed network.
System designers decided for over-the-air encryption only as they thought that the system itself is trustworthy. Thus, authentication of base stations against MSs was neglected, too. This opened ways to fake base stations. UMTS introduces full authentication of all components. Using less FEC These data rates are achievable using a single time-slot per frame in a certain channel.
HSCSD combines several time-slots but leaves coding untouched. GPRS can dynamically use several time-slots per frame plus offers 4 different coding schemes that allow for higher data rates per slot. While the standards in principle specify devices that use all 8 time-slots in both directions, real devices can often not send and receive at the same time.
Furthermore, older devices even need some time to switch from sending into receiving mode, thus wasting another slot or even several slots. Additionally, current GPRS phones often do not offer all coding schemes. The best average delay is 0. Assuming a data rate of TCP was made for streaming larger amounts of data, i.
TCP allows for fair sharing of bandwidth as soon as it is in stable state. This requires the reception of acknowledgements, the adaptation of sending windows and thresholds.
However, if the whole transfer is 10 kbyte only, TCP either never gets an acknowledgement back during transmission to adapt sender characteristics only if the initial sending window is large enough , or TCP wastes bandwidth by using a too small starting sending window standard case.
Real measurements with GPRS exhibit high latencies examples are round trip times for different packet sizes, class 8 mobile phone : 0. Additionally, measurements show high jitter. Under these conditions, TCP performs poorly.
Chapter 9 lists several proposed changes to TCP e. However, for data transfer the MSCs are not needed any more. Users can also apply SDM by placing access points further apart.
All the multiplexing schemes together result in very high capacities of the system, which is needed, e. Compared to GSM the system is simpler. Although data bases have been defined, too, typical DECT systems consist of a simple base station and several mobile devices.
Most scenarios do not require complicated handover although possible in DECT. Most systems furthermore do not need accounting and billing mechanisms as they are simply connected to the fixed phone network or a PBX. Trunked radio systems are attractive because of special features like very fast connection setup sub second , group calls, paging, high robustness, cheap operation, reliable and fast messaging, and ad-hoc capabilities.
Existing systems for these special purposes are still often analogue systems operating on special frequencies without strong encryption. This makes it very difficult to cooperate for, e. Trunked radio systems can be cheaper compared to GSM as they can have higher coverage with fewer base stations due to the lower expected load.
Furthermore, complex billing and accounting mechanisms are quite often not needed. Higher cell capacities and higher data rates are mainly achieved by more powerful modulation schemes, better codecs with higher compression rates for voice, CDMA as additional multiplexing scheme, and more powerful devices more precise power adaptation, utilisation of multipath propagation,.
UMTS implements asymmetrical data rates and different data rates in the same direction via different spreading factors. As the chipping rate of UMTS is always constant, data rates depend on the spreading factor.
The more the data is spread the lower the data rate is. Right now no one believes in a common worldwide system, not even the same frequencies are available everywhere: Europe: After a much discussed licensing process beauty contests and auctions many operators are currently deploying 3G systems. Some operators already dropped out, some filed bankruptcy. Although licensing did not prescribe the usage of UMTS, there were only a few operators thinking of different systems in the beginning.Therefore, However, this does not cause a collision but a simple denial of the connection request for several channels.
They must not block their position. Thus, there are no hidden or exposed terminals. This second authentication is much stronger compared to the PIN. If this terminal sends anyway it will not interfere as this terminal then acts as master with a different hopping sequence. Kindly Note: All signals must arrive synchronised at the base station, timing advance adjust the sending point the further away a terminal is the earlier it has to send its data.
This lets the CN directly send its data to the MN.
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