7/29/2019 HSPA Data Speeds

1/3

HSPA Data Speeds: Theoretical and Actual Rates

Overview

Mobile data speeds and capacity are increasingly

important for todays cellular operators. Data

traffic continues to grow at an exponential rate,

spurred by smartphones, new applications and

network capabilities.

Standards organizations and vendors compare

different data releases by looking at theoretical

rates and capabilities. While this is useful forcomparisons, it does not describe the actual data

rates users will experience. Modulation

techniques, coding rates, error correction and

information packet headers all utilize bandwidth

and lower the actual data rate throughput.

HSPA user data rates provide a clear example of

how actual data speeds are much lower than

theoretical speeds. While the industry defines

Release 6 HSPA as having a maximum

downlink (DL) data rate of 14.4 Mbps, userswill experience a far lower speed due to

technical requirements, network design and

environmental conditions. Data subscribers in

most HSPA markets typically experience an

average D/L speed of approximately 1 Mbps.

This paper discuss the why the practical and

actual data rates seen on commercial mobile

networks are lower than the theoretical speeds

listed in HSPA specifications.

Data Delivery Challenges

The market is demanding data. AT&T reported

that its mobile traffic increased 5000% over

three years. Ciscos global estimates show that

mobile data traffic increased 160% from

calendar year-end 2008 to calendar year-end

2009. Growth is being driven by several factors

including new high bandwidth applications, the

explosion of social media sites and a new class

of data friendly subscriber devices known as

smart phones. The industry continues to

provide higher speed mobile data network

solutions, including UTMS and HSPA to meet

the ever growing demand for mobile data

applications.

Theoretical Data Rates

Standards documents and vendors typically refer

to the theoretical rates when discussing mobile

data technologies. However, the theoretical

number can only be achieved in a lab

environment when there are no other users,

traffic or even overhead.

The theoretical data rates for UMTS/HSPA are

dependent on the specific standards release.

HSPA Release 6, for example, defines the

highest downlink (DL) rate as 14.4 Mbps, and

the uplink (UL) maximum rate as 5.7 Mbps.

Most U.S. cellular operators offer Release 6 data

speeds within their network, usually in urban or

heavily populated areas.

A theoretical data rate is determined by the

maximum throughput if there is one user close

to the antenna, and no overhead, signaling or

voice channels. That way the network can

HSPA Release 6 Maximum Theoretical D/LData Rate: 14.4 Mbps

7/29/2019 HSPA Data Speeds

2/3

Lemko Corporation www.lemko.com

allocate all of the power and code resources to

the single data terminal.

Unfortunately, mobile networks must have

overhead in order to properly function. Signaling

is required, and most operators must dedicate a

portion of the channels for voice traffic. This

results in a lower data speed for the user.

Practical Data Rates

In a commercial environment operators must

allocate bandwidth for quality issues, radio

frequency overhead and IP protocol overhead to

provide the quality of service subscribers expect.

A practical data rate takes these into account but

still utilizes all channels and bandwidth

available at the site (no voice traffic). The rate is

also impacted by the number of data users and

distance from the antenna.

Qualcomm University considers the practical

peak data rate to be 10.0 Mbps, about 30% lower

that the maximum theoretical data rate. They

state the peak rate is observed when there is only

one data user and no voice channels. It still

requires good RF conditions and a full capability

user device capable of supporting the high rate.

Other vendors and industry experts agree with

Qualcomm.

From a technical perspective, the data

throughput is affected by the modulation

technique and the effective coding rate. HSPA

uses 16 QAM modulation and a effective

coding rate. Based on the technical limitations

and structure of this design, the best practicaldata rate in a lab environment will be

approximately 10.7 Mbps. Once other factors

like overhead are considered the rate drops to

near 10 Mbps. (Source: Qualcomm University,

WCDMA for UMTS)

There are several functions that consume the

4Mbps of capacity between theoretical and

practical. Radio frequency (RF) overhead is

required to minimize errors and interference that

negatively affect the user experience. Specificbandwidth consuming items include forward

error correction, re-ordering the re-transmission

packets and signal-to-noise ratio compensation.

All take up bit capacity, lowering the

maximum possible data speed. Additionally, an

operator must allocate capacity for their ACK

or acknowledgement time. These are required to

deliver the quality of service and experience

subscribers expect.

Actual Data Rates

Operators must continue to provide voice and

SMS text services along with HSPA data. Many

cell sites are configured to support 50% voice

traffic, and 50% data traffic. In this real world

configuration, all practical data rates are halved

as only half of the bandwidth is allocated for

data applications. Therefore the highest data rate

a single user might experience is approximately5 Mbps. In scenarios where there are numerous

users, the highest average rate would be the 5

Mbps / Number-of-Users.

Theoretical D/L Peak Rate: 14.4 MbpsModulation, Coding Impact -3.7 MbpsIP Headers, Other Overhead: -0.7 Mbps

Practical D/L Peak Rate: 10.0 Mbps

7/29/2019 HSPA Data Speeds

3/3

Lemko Corporation www.lemko.com

Data speeds are affected by physical and

environmental factors within each network.

Distance from the cell site antenna, line of site

items and even weather lower the actual data

speed.Therefore, operators must carefully plan

their network to accommodate for geographical

and physical limitations, and set user

expectations accordingly.

Observed Industry Data Speeds

PC Magazine completed a mobile broadbandstudy in May, 2010. They tested the data rates of

all major U.S. carriers by using two laptops with

modems to test the mobile Internet experience.

PC Magazine ran approximately 1,000 tests in

20 different cities. Results of their study are

contained in the June 3, 2010 edition of their

magazine.

In summary, the average downlink speed across

the four largest cellular carriers ranged from .99

Mbps to 1.79 Mbps. It should be noted that the

higher speeds were observed in cities where

HSPA+ is deployed. Network specific

information is contained in the table below. The

speeds are averages across all cities where their

data service was tested.

Carrier ConsistencyD/L speed

(Mbps)

Timeto firstbyte

(Pct) Avg Max (Sec)

AT&T 86.2 1.72 2.75 1.00

Cricket 95.32 0.94 1.54 1.06

Sprint 3G 95.9 0.99 1.26 1.12

T-Mobile 92.78 1.17 2.26 1.21

Verizon 88.22 1.01 1.4 1.02

3G Data Speeds on Commercial Networks(Source: PC Magazine, June, 2010)

Clearly, data subscribers across the nation,

regardless of carrier, are experiencing actual

data rates far lower than the touted 14.4Mbps

theoretical rate. The network and its resources

must be shared with voice and multiple data

users. People access the network in locations

which distant from the cell site. Numerous users

contend for the same bandwidth on a regular

basis. The real world average data speed

experience on an HSPA network is much closer

to 1 Mbps.

Conclusion

Third generation HSPA Release 6 is touted as

providing a maximum downlink data rate 14.4

Mbps. The actual maximum data rate is affected

by inherent overhead, coding factors, the

number of voice channels, number of data users

and geographic considerations. A single data

session may experience up to 10 Mbps in perfect

lab conditions when all channels are allocated

for data. Actual subscribers on a network that

support voice and data will experience downlink

speeds ranging from 1Mbps to 5Mbps.

50% Voice; 50% Data Configuration,Single User, Ideal Conditions

Actual Maximum D/L Rate: 5 Mb s