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Figure 6Mapping of higher layer packets onto the layers of HIPERLAN/2.sible to standardize and implement the DLCand PHY layers independently of the corenetwork. Figure 6 depicts the mapping ofhigher-layer data uni ts down to PHY bursts.For transmission, the data units on the DLClayer are long transport channel (LCH) packetdata units (PDU); for control messages,short transport channel (SCH) PDUs areused.DLC layerThe DLC layer consists of a radio link control(RLC) sublayer, an error control (EC)protocol, and a MAC protocol.RLC sublayerThe RLC handles three main control functions:1. The association control function is usedfor authentication, key management, association,disassociation, and encryptionseed.2.The radio resource control (RRC) functionmanages handover (generic solution),dynamic frequency selection, mobile terminalalive/absent, power saving, andpower control.3. The DLC user-connection control functionsets up and releases user connections,multicast and broadcast.In summary, the RLC is used for exchangingdata in the control plane between an accesspoint and a mobile terminal—for instance,the mobile terminal forms associationswith the access point via RLC signaling.After completing the association procedure,the mobile terminal can request adedicated control channel for setting upradio bearers. Within the HIPERLAN/2specification, radio bearers are referred to asDLC connections. The mobile terminalmight even request multiple DLC connections,each offering unique support for qualityof service (QoS) as determined by the accesspoint.Set-up of the connection does not necessarilyresult in immediate assignment of capacityby the access point. Instead, the mobileterminal receives a unique DLC addressthat corresponds to the DLC connection.ErrorcontrolThe error control modes of operation are definedto support different types of service:1. The acknowledged mode uses retransmissionto improve link quality and guarantee reliabletransmission. The acknowledgedmode is based on selective-repeat (SR) automaticrepeat request (ARQ)." Low latencycan be provided by means of a discardmechanism.2.The repetition mode repeats the databearingDLC PDUs (LCH PDU) to providefairly reliable transmission (Figure4). No feedback channel is available. Thetransmitter can arbitrarily retransmitPDUs. The retransmission of PDUs enhancesreception. However, the receiveronly accepts PDUs whose sequence numbersare within its acceptance window.The repetition mode is typically used fortransmitting broadcast data.3. The unacknowledged mode provides unreliable,low-latency communication withoutretransmissions. Hence, no feedbackchannel is available.4.Unicast data can be sent using either acknowledgedor unacknowledged mode.Broadcast services can be supported by eitherrepetition mode or unacknowledgedmode. Multicast services can be sent inunacknowledged mode or they can bemultiplexed onto existing unicast transmissions.MACThe basic frame structure on the air interfacehas a fixed duration of 2 ms and comprisesfields for broadcast control, frame control,access feedback control, data transmissionin the downlink and uplink, and randomaccess (Figure 7). During direct-linkcommunication, the frame contains an ad-112 Ericsson Review No. 2, 2000
Figure 7Basic frame structure (one-sectorantenna).ditional direct-link field (not shown in Figure7). The duration of broadcast control isfixed, whereas the duration of other fields isdynamically adapted to the traffic situation.The broadcast channel (BCH), which containscontrol information that is sent inevery MAC frame, mainly enables the controlof radio resources. The frame channel(FCH) contains an exact description of theallocation of resources within the currentMAC frame. The access feedback channel(ACH) conveys information on previous attemptsat random access. Downlink or uplinktraffic consists of data to or from mobileterminals. Traffic from multiple connectionsto or from a mobile terminal canbe multiplexed onto one PDU train, whereeach connection contains 54-octet LCHs fordata and 9-octet SCHs for control messages.HIPERLAN/2 supports multibeam antennas(sectors) as a means of improving thelink budget and of reducing interference inthe radio network. The MAC protocol andthe frame structure in HIPERLAN/2 supportmultibeam antennas with up to eightbeams (not shown in Figure 7).When a mobile terminal has data to transmiton a certain DLC connection, it mustfirst request capacity by sending a resourcerequest (RR) to the access point. The resourcerequest contains the number of pendingLCH PDUs in the mobile terminal forthe particular DLC connection. Based on aslotted scheme, the mobile terminal can usecontention slots to send the RR message. Byvarying the number of contention slots (randomaccess channels, RCH), the access pointcan decrease access delay. If a collision occurs,the mobile terminal is informed in theACH of the next MAC frame. The mobileterminal then backs off a random number ofaccess slots.After sending the resource request to theaccess point, the mobile terminal enters acontention-free mode where it is scheduledfor transmission opportunities (uplink anddownlink). The scheduling of resources isperformed in the access point—a centralizedcontroller enables efficient QoS support.From time to time the access point mightpoll the mobile terminal for information onpending PDUs. Similarly, the mobile terminalmight inform the access point of itsstatus by sending a resource request via theRCH.Radio network functions and QoS supportThe HIPERLAN/2 standard defines measurementsand signaling that support anumber of radio-network functions, includingdynamic frequency selection, link adaptation,handover, multibeam antennas, andpower control. The algorithms are vendorspecific.The supported radio-network functionsallow the cellular deployment ofHIPERLAN/2 systems with full coverageand high data rates in a variety of environments.The system automatically allocatesfrequencies to each access point for communication—dynamicfrequency selection(DFS) allows several operators to share availablespectrum and avoids the use of interferedfrequencies. Frequency selection isbased on interference measurements performedby the access point and associatedmobile terminals. 12The quality of the radio link, which is dependenton the radio environment, changesEricsson Review No. 2, 2000 113
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Ericsson 2/2000REVIEWTHE TELECOMMUN
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ContributorsIn this issueLuis Barri
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Ericsson Review is also published o
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Evolving from cdmaOne to third-gene
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Figure 2Operators Harmonization Agr
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Page 14 and 15: Figure 7Ericsson's third-generation
Page 16 and 17: Figure 11Ericsson's timeline for ev
Page 18 and 19: Third-generation TDMAChristofer Lin
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Page 24 and 25: Figure 5Curves illustrating maximum
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Page 30 and 31: Business solutions for mobile e-com
Page 32 and 33: Figure 2Comparison of traditional a
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Page 36 and 37: Figure 6Mobile e-Pay end-user servi
Page 38 and 39: Figure 8Access features with push-a
Page 40 and 41: AuthenticationTo verify that end-us
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Page 44 and 45: Figure 2The footprint of the RBS 22
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Page 56 and 57: TRADEMARKSRC4 and RC4 are registere
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Page 64 and 65: TABLE 1PHYSICAL LAYER MODES OF HIPE
Page 66 and 67: Queen City WaterfrontEMERGING PROJE
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