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The future of wireless networks lies in the coexistence of multiple access network technologies. This paper deals with two data oriented access networks, the worldwide interoperability for microwave access (WiMAX) and the high speed downlink packet access (HSDPA). HSDPA and Mobile WiMAX are two different high speed mobile technologies with distinctive backgrounds. WiMAX is based on OFDM as HSDPA is based on CDMA.
The objective of this paper is to provide a techno-economic comparison of two wireless broadband technologies, Mobile WiMAX and HSDPA. The comparison is divided into two parts. The first part is a general overview and comparison of the two technology standards. The second part describes the different releases of WiMAX and HSDPA and the market opportunities.
What is WiMAX?
WiMAX is the new term for IEEE 802.16 STANDARD. It is based on the wireless MAN technology. It is a communication technology that works with the radio spectrum to transmit tens of MB/sec in bandwidth between different devices like laptops. The two stimulating forces of present internet are the wireless and the broadband. The WiMAX standard joins the two high speed broadband internet access over a single wireless connection. As WiMAX can be used for long distance purposes it is a very effective way to solve the last mile problem. WiMAX would operate similar to a Wi-Fi but at higher speeds, large distance and for more number of users. WiMAX has the capability to provide service in areas which are difficult for wired infrastructure to reach and has the ability to overcome the limitations of the traditional wired infrastructure. It will provide wireless broadband access to the buildings, either to existing wired networks or in the rural areas. It can also be connected to the WLAN hotspots to the internet.
Some of the characteristics of Mobile WiMAX are:
- Scalability: Mobile WiMAX has been framed in such a way that it is able to work in different channel BW's ranging from 1.25 to 20 MHz.
- High Data Rates: when Maximum Input Maximum Output (MIMO) 2*2 is used and DL: UL is in the ratio of 1:0 and 0:1 respectively, in a 10 MHz channel high data rates can theoretically support peak download data rates up to 63Mb/s per sector and peak upload data rates up to 28 Mb/s per sector.
- Mobility: Seamless handoff which is less than 50ms latency and < 1% packet loss is supported. Upto 120 km/hr of mobility has been tested for Mobile WiMAX.
- Quality of Service (QoS): QoS measures for WiMAX include availability of service, throughput of data, jitter and the rate of error.
WHAT IS HSDPA?
High speed Downlink packet access (HSDPA) is a packet based data service feature of the WCDMA standard. In the WCDMA downlink, the data transmission is up to 8-10 Megabits/sec over a bandwidth of 5MHZ. It is sometimes referred to as a 3.5G technology. HSDPA is an advancement of the WCDMA standard which is created to increase the data rate by a factor of 5 or more. HSDPA improves on W-CDMA by using different techniques for modulation and coding. It defines a new WCDMA called high-speed downlink shared channel (HS-DSCH). That channel performs contrastingly from other channels and helps to fasten the downlink speeds. HS-DSCH is used only for the downlink communication of the mobile. That means that data is sent from the source to the phone. It isn't possible to send data from the phone to a source using HSDPA. The channel is shared between all users which lets the radio signals to be used most effectively for the fastest downloads.
The security service in a WiMAX is used by an operator to gain benefits from this service as there is always a chance of theft of service in connections, bandwidth and so on. Hence the security service is divided into two parts namely the encryption and the authentication/key derivation. WiMAX supports modern cryptographic algorithms.
In HSDPA, Users are authorized by their SIM (or R-UIM) cards. HSDPA does not provide any additional security functions. Typical of all CDMA standards, data encoding for various users works better than any cryptographic algorithm, but doesn't work if an interrupter somehow gets its channels code (like special agents) or is in a base station. Whereas, in WiMAX the base station is strongly protected from management attacks and as the system is organized strongly a certificate based security is easy to deploy and is advisable.
When HSDPA and WiMAX are at same distance from a base station, the gain in HSDPA vs. WiMAX is not clear yet. One of the main reasons for this is WiMAX doesn't have many frequency ranges. But if HSDPA, being an evolutional step in the development of WCDMA, is getting close to the threshold of spectral efficiency, while WiMAX has many likely ways of progression such as new modulation schemes (as well combined with the old ones),MIMO(multiple-input-multiple output)and new frequency ranges (ranging from 10GHz to 66GHz).
With the use of a robust modulation scheme at long ranges with high spectral efficiency WiMAX gives tremendous throughput and also bears multipath fading. WiMAX base station interchanges throughput for range and this is allowed by the dynamic adaptive modulation. HSDPA supports 16 QAM and QPSK modulation whereas WiMAX supports QPSK, 16 QAM and 64 QAM. This implies that Mobile WiMAX supports higher order modulation than HSDPA. With 64 QAM 6 bits can be carried per symbol and thus higher data rates can be achieved.