64 QAM Constellation View
A constellation diagram for rectangular 16-QAM
A constellation diagram is a representation of a signal modulated by a digital modulation scheme such as quadrature amplitude modulation or phase-shift keying. It displays the signal as a two-dimensional scatter diagram in the complex plane at symbol sampling instants. In a more abstract sense, it represents the possible symbols that may be selected by a given modulation scheme as points in the complex plane. Measured constellation diagrams can be used to recognize the type of interference and distortion in a signal. (http://en.wikipedia.org/wiki/Constellation_diagram.)
Quadrature amplitude modulation:
UMTS Long Term Evolution (LTE) Technology Introduction
Even with the introduction of HSPA, evolution of UMTS has not reached its end. To ensure the competitiveness of UMTS for the next 10 years and beyond, UMTS Long Term Evolution (LTE) has been introduced in 3GPP release 8. LTE, which is also known as Evolved UTRA and Evolved UTRAN, provides new physical layer concepts and protocol architecture for UMTS. This application note introduces LTE technology and testing aspects.
Currently, UMTS networks worldwide are being upgraded to High Speed packet Access (HSPA) in order to increase data rate and capacity for packet data. HSPA refers to the combination of High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA).
While HSDPA was introduced as a 3GPP release 5 feature, HSUPA is an
important feature of 3GPP release 6. However, even with the introduction of HSPA, evolution of UMTS has not reached its end. HSPA+ will bring significant enhancements in 3GPP release 7. Objective is to enhance performance of HSPA based radio networks in terms of spectrum efficiency, peak data rate and latency, and exploit the full potential of WCDMA based 5 MHz operation. Important features of HSPA+ are downlink MIMO (Multiple Input Multiple Output), higher order modulation for uplink and downlink, improvements of layer 2 protocols, and continuous packet connectivity.
In order to ensure the competitiveness of UMTS for the next 10 years and beyond, concepts for UMTS Long Term Evolution (LTE) have been introduced in 3GPP release 8. Objective is a high-data-rate, low-latency and packet-optimized radio access technology. LTE is also referred to as E-UTRA (Evolved UMTS Terrestrial Radio Access) or E-UTRAN (Evolved UMTS Terrestrial Radio Access Network).
This application note focuses on LTE/E-UTRA technology. In the following,
the terms LTE or E-UTRA are used interchangeably. LTE has ambitious requirements for data rate, capacity, spectrum efficiency, and latency. In order to fulfill these equirements, LTE is based on new technical principles. LTE uses new multiple access schemes on the air interface: OFDMA (Orthogonal Frequency Division Multiple Access) in
downlink and SC-FDMA (Single Carrier Frequency Division Multiple Access) in uplink.
Furthermore, MIMO antenna schemes form an essential part of LTE. In order to simplify protocol architecture, LTE brings some major changes to the existing UMTS protocol concepts. Impact on the overall network architecture including the core network is referred to as 3GPP System Architecture Evolution (SAE).
Requirements for UMTS Long Term Evolution
LTE is focusing on optimum support of Packet Switched (PS) Services. Main requirements for the design of an LTE system have been captured in 3GPP TR 25.913  and can be summarized as follows:
- Data Rate: Peak data rates target 100 Mbps (downlink) and 50 Mbps (uplink) for 20 MHz spectrum allocation, assuming 2 receive antennas and 1 transmit antenna at the terminal.
- Throughput: Target for downlink average user throughput per MHz is 3-4 times better than release 6. Target for uplink average user throughput per MHz is 2-3 times better than release 6.
- Spectrum Efficiency: Downlink target is 3-4 times better than release 6. Uplink target is 2-3 times better than release 6.
- Latency: The one-way transit time between a packet being available at the IP layer in either the UE or radio access network and the availability of this packet at IP layer in the radio access network/UE shall be less than 5 ms. Also C-plane latency shall be reduced, e.g. to allow fast transition times of less than 100 ms from camped state to active state.
- Bandwidth: Scaleable bandwidths of 5, 10, 15, 20 MHz shall be supported. Also bandwidths smaller than 5 MHz shall be supported for more flexibility, i.e. 1.4 MHz and 3 MHz for FDD mode.
- Interworking: Interworking with existing UTRAN/GERAN systems and non-3GPP systems shall be ensured. Multimode terminals shall support handover to and from UTRAN and GERAN as well as inter-RAT measurements. Interruption time for handover between E-UTRAN and UTRAN/GERAN shall be less than 300 ms for real time services and less than 500 ms for non real time services.
- Multimedia Broadcast Multicast Services (MBMS): MBMS shall be further enhanced and is then referred to as E-MBMS.
- Costs: Reduced CAPEX and OPEX including backhaul shall be achieved. Cost effective migration from release 6 UTRA radio interface and architecture shall be possible. Reasonable system and terminal complexity, cost and power consumption shall be ensured. All the interfaces specified shall be open for multi-vendor equipment
- Mobility: The system should be optimized for low mobile speed (0-15 km/h), but higher mobile speeds shall be supported as well including high speed train environment as special case.
- Spectrum allocation: Operation in paired (Frequency Division Duplex / FDD mode) and unpaired spectrum (Time Division Duplex / TDD mode) is possible.
- Co-existence: Co-existence in the same geographical area and co-location with GERAN/UTRAN shall be ensured. Also, co-existence between operators in adjacent bands as well as cross-border co-existence is a requirement.
- Quality of Service: End-to-end Quality of Service (QoS) shall be supported. VoIP should be supported with at least as good radio andbackhaul efficiency and latency as voice traffic over the UMTS circuit switched networks.
- Network synchronization: Time synchronization of different network sites shall not be mandated.
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